x86-64: software IRQ masking and handling

Hello,

This is something suggested by Rusty Russell a while ago. It makes IRQ masking a software switch like preemption or softirq enable/disable. Hardware interrupt masking (cli/sti) and delivery are decoupled from actual IRQ handling. IRQ disabling is done by single instruction moving 1 to a percpu variable. Enabling is similar but it should check whether there's any pending interrupt to handle.

This change greatly reduces the number of hardware IRQ masking manipulations. cli/sti still being somewhat costly operations (I hear nehalem is better tho), this should be able to improve overall performance, especially on paravirts.

I just got it working and it behaves pretty good on qemu.  Actual machines can't idle but seem to work otherwise.  I'll fix up idle, get paravirt working and try to get some perf measurements but I'll be mostly off next week, so it will take some time.  In the meantime, what do you guys think?

Thanks.

HIGHLY_EXPERIMENTAL_DONT_APPLY
---
 arch/x86/ia32/ia32entry.S       |   12 +-- arch/x86/include/asm/irqflags.h |  103 ++++++++++++++++++++++------ arch/x86/include/asm/paravirt.h |   21 +---- arch/x86/include/asm/system.h   |    4 - arch/x86/kernel/cpu/common.c    |   10 ++ arch/x86/kernel/entry_64.S      |  143 +++++++++++++++++++++++++--------------- arch/x86/kernel/irq.c           |   21 +++++ arch/x86/kernel/process.c       |   21 ++--- arch/x86/kernel/process_64.c    |    2
 arch/x86/kernel/smpboot.c       |    2
 arch/x86/kernel/traps.c         |   16 ++--
 arch/x86/mm/fault.c             |    6 - drivers/acpi/processor_idle.c   |   24 +++--- drivers/cpuidle/cpuidle.c       |    6 -
 include/linux/irqflags.h        |   31 ++++++++
 init/main.c                     |    2
 lib/smp_processor_id.c          |    2

 17 files changed, 283 insertions(+), 143 deletions(-)

Index: work/drivers/acpi/processor_idle.c
===================================================================

drivers/acpi/processor_idle.c +12 -12

@@ -137,7 +137,7 @@ static void acpi_safe_halt(void)
        smp_mb();
        if (!need_resched()) {
                safe_halt();
-               local_irq_disable();
+               hw_irq_disable();
        }
        current_thread_info()->status |= TS_POLLING;
  }

@@ -826,11 +826,11 @@ static int acpi_idle_enter_c1(struct cpu
        if (unlikely(!pr))
                return 0;
 
-       local_irq_disable();
+       hw_irq_disable();
 
        /* Do not access any ACPI IO ports in suspend path */
        if (acpi_idle_suspend) {
-               local_irq_enable();
+               hw_irq_enable();
                cpu_relax();
                return 0;
        }

@@ -841,7 +841,7 @@ static int acpi_idle_enter_c1(struct cpu
        kt2 = ktime_get_real();
        idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
 
-       local_irq_enable();
+       hw_irq_enable();
        cx->usage++;
        lapic_timer_state_broadcast(pr, cx, 0);
 

@@ -870,7 +870,7 @@ static int acpi_idle_enter_simple(struct
        if (acpi_idle_suspend)
                return(acpi_idle_enter_c1(dev, state));
 
-       local_irq_disable();
+       hw_irq_disable();
 
        if (cx->entry_method != ACPI_CSTATE_FFH) {
                current_thread_info()->status &= ~TS_POLLING;

@@ -882,7 +882,7 @@ static int acpi_idle_enter_simple(struct
 
                if (unlikely(need_resched())) {
                        current_thread_info()->status |= TS_POLLING;
-                       local_irq_enable();
+                       hw_irq_enable();
                        return 0;
                }
        }

@@ -908,7 +908,7 @@ static int acpi_idle_enter_simple(struct
        /* Tell the scheduler how much we idled: */
        sched_clock_idle_wakeup_event(idle_time_ns);
 
-       local_irq_enable();
+       hw_irq_enable();
        if (cx->entry_method != ACPI_CSTATE_FFH)
                current_thread_info()->status |= TS_POLLING;
 

@@ -952,14 +952,14 @@ static int acpi_idle_enter_bm(struct cpu
                        dev->last_state = dev->safe_state;
                        return dev->safe_state->enter(dev, dev->safe_state);
                } else {
-                       local_irq_disable();
+                       hw_irq_disable();
                        acpi_safe_halt();
-                       local_irq_enable();
+                       hw_irq_enable();
                        return 0;
                }
        }
 
-       local_irq_disable();
+       hw_irq_disable();
 
        if (cx->entry_method != ACPI_CSTATE_FFH) {
                current_thread_info()->status &= ~TS_POLLING;

@@ -971,7 +971,7 @@ static int acpi_idle_enter_bm(struct cpu
 
                if (unlikely(need_resched())) {
                        current_thread_info()->status |= TS_POLLING;
-                       local_irq_enable();
+                       hw_irq_enable();
                        return 0;
                }
        }

@@ -1025,7 +1025,7 @@ static int acpi_idle_enter_bm(struct cpu
        /* Tell the scheduler how much we idled: */
        sched_clock_idle_wakeup_event(idle_time_ns);
 
-       local_irq_enable();
+       hw_irq_enable();
        if (cx->entry_method != ACPI_CSTATE_FFH)
                current_thread_info()->status |= TS_POLLING;
 

Index: work/drivers/cpuidle/cpuidle.c
===================================================================

drivers/cpuidle/cpuidle.c +3 -3

@@ -61,7 +61,7 @@ static void cpuidle_idle_call(void)
  #if defined(CONFIG_ARCH_HAS_DEFAULT_IDLE)
                        default_idle();
  #else
-                       local_irq_enable();
+                       hw_irq_enable();
  #endif
                return;
        }

@@ -77,7 +77,7 @@ static void cpuidle_idle_call(void)
        /* ask the governor for the next state */
        next_state = cpuidle_curr_governor->select(dev);
        if (need_resched()) {
-               local_irq_enable();
+               hw_irq_enable();
                return;
        }
 

@@ -229,7 +229,7 @@ static int poll_idle(struct cpuidle_devi
        int ret;
 
        t1 = ktime_get();
-       local_irq_enable();
+       hw_irq_enable();
        while (!need_resched())
                cpu_relax();
 

Index: work/include/linux/irqflags.h
===================================================================

include/linux/irqflags.h +31 -0

@@ -79,6 +79,17 @@
                        raw_local_irq_restore(flags);   \
                }                                       \
        } while (0)
+
+#ifndef __ARCH_HAS_HW_IRQ
+#define raw_hw_irq_enable()            raw_local_irq_enable()
+#define raw_hw_irq_disable()           raw_local_irq_disable()
+#endif
+
+#define hw_irq_enable() \
+       do { trace_hardirqs_on(); raw_hw_irq_enable(); } while (0)
+#define hw_irq_disable() \
+       do { raw_hw_irq_disable(); trace_hardirqs_off(); } while (0)
+
  #else /* !CONFIG_TRACE_IRQFLAGS_SUPPORT */
  /*
  * The local_irq_*() APIs are equal to the raw_local_irq*()

@@ -96,6 +107,10 @@
                typecheck(unsigned long, flags);        \
                local_irq_restore(flags);               \
        } while (0)
+# define raw_hw_irq_enable()           raw_local_irq_enable()
+# define raw_hw_irq_disable()          raw_local_irq_disable()
+# define hw_irq_enable()               raw_hw_irq_enable()
+# define hw_irq_disable()              raw_hw_irq_disable()
  #endif /* CONFIG_TRACE_IRQFLAGS_SUPPORT */
 
  #ifdef CONFIG_TRACE_IRQFLAGS_SUPPORT

@@ -124,6 +139,22 @@
        typecheck(unsigned long, flags);        \
        raw_irqs_disabled_flags(flags);         \
  })
+
+#ifdef __ARCH_HAS_HW_IRQ
+static inline bool hw_irqs_disabled(void)
+{
+       unsigned long flags;
+
+       if (irqs_disabled())
+               return true;
+
+       raw_hw_irq_save_flags(flags);
+       return raw_hw_irqs_disabled_flags(flags);
+}
+#else  /* __ARCH_HAS_HW_IRQ */
+#define hw_irqs_disabled()             irqs_disabled()
+#endif /* __ARCH_HAS_HW_IRQ */
+
  #endif /* CONFIG_TRACE_IRQFLAGS_SUPPORT */
 
  #endif

Index: work/init/main.c
===================================================================

init/main.c +0 -0

@@ -626,7 +626,7 @@ asmlinkage void __init start_kernel(void

               printk(KERN_CRIT "start_kernel(): bug: interrupts were " "enabled early\n"); early_boot_irqs_on();
-       local_irq_enable();
+       hw_irq_enable();

       /* Interrupts are enabled now so all GFP allocations are safe. */ gfp_allowed_mask = __GFP_BITS_MASK;
Index: work/arch/x86/include/asm/system.h
===================================================================

arch/x86/include/asm/system.h +2 -2

@@ -102,8 +102,8 @@ do {                                                                        \
  #define __RESTORE(reg, offset) "movq (14-" #offset ")*8(%%rsp),%%" #reg "\n\t"
 
  /* frame pointer must be last for get_wchan */
-#define SAVE_CONTEXT    "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t"
-#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t"
+#define SAVE_CONTEXT    "pushq %%rbp ; movq %%rsi,%%rbp\n\t"
+#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\t"
 
  #define __EXTRA_CLOBBER  \
        , "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \

Index: work/arch/x86/ia32/ia32entry.S
===================================================================

arch/x86/ia32/ia32entry.S +1 -1

@@ -162,7 +162,7 @@ sysenter_dispatch:
        movq    %rax,RAX-ARGOFFSET(%rsp)
        GET_THREAD_INFO(%r10)
        DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
        testl   $_TIF_ALLWORK_MASK,TI_flags(%r10)

       jnz     sysexit_audit
 sysexit_from_sys_call:

arch/x86/ia32/ia32entry.S +0 -0

@@ -182,7 +182,7 @@ sysexit_from_sys_call:

       popq    %rcx                            /* User %esp */ CFI_ADJUST_CFA_OFFSET -8
       CFI_REGISTER rsp,rcx
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       ENABLE_INTERRUPTS_SYSEXIT32

 #ifdef CONFIG_AUDITSYSCALL

arch/x86/ia32/ia32entry.S +0 -0

@@ -207,7 +207,7 @@ sysexit_from_sys_call:

       .macro auditsys_exit exit
       testl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),TI_flags(%r10) jnz ia32_ret_from_sys_call
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       sti
       movl %eax,%esi          /* second arg, syscall return value */ cmpl $0,%eax            /* is it < 0? */

arch/x86/ia32/ia32entry.S +0 -0

@@ -219,7 +219,7 @@ sysexit_from_sys_call:

       movl RAX-ARGOFFSET(%rsp),%eax   /* reload syscall return value */ movl $(_TIF_ALLWORK_MASK & ~_TIF_SYSCALL_AUDIT),%edi cli
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       testl %edi,TI_flags(%r10)
       jz \exit
       CLEAR_RREGS -ARGOFFSET

arch/x86/ia32/ia32entry.S +1 -1

@@ -323,7 +323,7 @@ cstar_dispatch:
        movq %rax,RAX-ARGOFFSET(%rsp)
        GET_THREAD_INFO(%r10)
        DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
        testl $_TIF_ALLWORK_MASK,TI_flags(%r10)

       jnz sysretl_audit
 sysretl_from_sys_call:

arch/x86/ia32/ia32entry.S +0 -0

@@ -336,7 +336,7 @@ sysretl_from_sys_call:

       xorq    %r10,%r10
       xorq    %r9,%r9
       xorq    %r8,%r8
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       movl RSP-ARGOFFSET(%rsp),%esp
       CFI_RESTORE rsp
       USERGS_SYSRET32
Index: work/arch/x86/kernel/cpu/common.c
===================================================================

arch/x86/kernel/cpu/common.c +9 -1

@@ -1005,6 +1005,14 @@ DEFINE_PER_CPU(char *, irq_stack_ptr) =
 
  DEFINE_PER_CPU(unsigned int, irq_count) = -1;
 
+DEFINE_PER_CPU(unsigned int, x86_irq_enable) = 0;
+EXPORT_PER_CPU_SYMBOL(x86_irq_enable);
+
+DEFINE_PER_CPU(unsigned long, x86_irq_pending) = 0;
+EXPORT_PER_CPU_SYMBOL(x86_irq_pending);
+
+DEFINE_PER_CPU(void (*)(struct pt_regs *), x86_irq_pending_handler) = NULL;
+
  /*
  * Special IST stacks which the CPU switches to when it calls
  * an IST-marked descriptor entry. Up to 7 stacks (hardware

@@ -1211,7 +1219,7 @@ void __cpuinit cpu_init(void)
        if (cpumask_test_and_set_cpu(cpu, cpu_initialized_mask)) {
                printk(KERN_WARNING "CPU#%d already initialized!\n", cpu);
                for (;;)
-                       local_irq_enable();
+                       hw_irq_enable();
        }
 
        printk(KERN_INFO "Initializing CPU#%d\n", cpu);

Index: work/arch/x86/kernel/entry_64.S
===================================================================

arch/x86/kernel/entry_64.S +1 -1

@@ -175,11 +175,11 @@ ENDPROC(native_usergs_sysret64)
  #endif /* CONFIG_PARAVIRT */
 
 
-.macro TRACE_IRQS_IRETQ offset=ARGOFFSET
+.macro TRACE_HW_IRQS_IRETQ offset=ARGOFFSET
  #ifdef CONFIG_TRACE_IRQFLAGS

       bt   $9,EFLAGS-\offset(%rsp)    /* interrupts off? */ jnc  1f
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
 1:
 #endif
 .endm

arch/x86/kernel/entry_64.S +0 -0

@@ -317,17 +317,14 @@ ENTRY(save_args)

       leaq -ARGOFFSET+16(%rsp),%rdi   /* arg1 for handler */ movq_cfi rbp, 8         /* push %rbp */
       leaq 8(%rsp), %rbp              /* mov %rsp, %ebp */
-       testl $3, CS(%rdi)
-       je 1f
-       SWAPGS
       /*
        * irq_count is used to check if a CPU is already on an interrupt stack
        * or not. While this is essentially redundant with preempt_count it is
        * a little cheaper to use a separate counter in the PDA (short of
        * moving irq_enter into assembly, which would be too much work) */
-1:     incl PER_CPU_VAR(irq_count)
-       jne 2f
+       incl PER_CPU_VAR(irq_count)
+       jne 1f
       popq_cfi %rax                   /* move return address... */ mov PER_CPU_VAR(irq_stack_ptr),%rsp
       EMPTY_FRAME 0

arch/x86/kernel/entry_64.S +1 -1

@@ -336,7 +333,7 @@ ENTRY(save_args)
        /*
         * We entered an interrupt context - irqs are off:
         */
-2:     TRACE_IRQS_OFF
+1:     TRACE_HW_IRQS_OFF

       ret
       CFI_ENDPROC
 END(save_args)

arch/x86/kernel/entry_64.S +0 -0

@@ -497,7 +494,7 @@ sysret_check:

       LOCKDEP_SYS_EXIT
       GET_THREAD_INFO(%rcx)
       DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       movl TI_flags(%rcx),%edx
       andl %edi,%edx
       jnz  sysret_careful

arch/x86/kernel/entry_64.S +1 -1

@@ -505,7 +502,7 @@ sysret_check:
        /*
         * sysretq will re-enable interrupts:
         */
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON

       movq RIP-ARGOFFSET(%rsp),%rcx
       CFI_REGISTER    rip,rcx
       RESTORE_ARGS 0,-ARG_SKIP,1

arch/x86/kernel/entry_64.S +0 -0

@@ -519,7 +516,7 @@ sysret_check:

 sysret_careful:
       bt $TIF_NEED_RESCHED,%edx
       jnc sysret_signal
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       ENABLE_INTERRUPTS(CLBR_NONE)
       pushq %rdi
       CFI_ADJUST_CFA_OFFSET 8

arch/x86/kernel/entry_64.S +0 -0

@@ -530,7 +527,7 @@ sysret_careful:
 
        /* Handle a signal */

 sysret_signal:
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       ENABLE_INTERRUPTS(CLBR_NONE)
 #ifdef CONFIG_AUDITSYSCALL
       bt $TIF_SYSCALL_AUDIT,%edx

arch/x86/kernel/entry_64.S +1 -1

@@ -612,7 +609,7 @@ tracesys:
  */
  GLOBAL(int_ret_from_sys_call)
        DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
        testl $3,CS-ARGOFFSET(%rsp)

       je retint_restore_args
       movl $_TIF_ALLWORK_MASK,%edi

arch/x86/kernel/entry_64.S +0 -0

@@ -632,7 +629,7 @@ GLOBAL(int_with_check)

 int_careful:
       bt $TIF_NEED_RESCHED,%edx
       jnc  int_very_careful
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       ENABLE_INTERRUPTS(CLBR_NONE)
       pushq %rdi
       CFI_ADJUST_CFA_OFFSET 8

arch/x86/kernel/entry_64.S +0 -0

@@ -640,12 +637,12 @@ int_careful:

       popq %rdi
       CFI_ADJUST_CFA_OFFSET -8
       DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       jmp int_with_check

       /* handle signals and tracing -- both require a full stack frame */ int_very_careful:
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       ENABLE_INTERRUPTS(CLBR_NONE) int_check_syscall_exit_work:
       SAVE_REST

arch/x86/kernel/entry_64.S +0 -0

@@ -671,7 +668,7 @@ int_signal:

 int_restore_rest:
       RESTORE_REST
       DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       jmp int_with_check
       CFI_ENDPROC
 END(system_call)

arch/x86/kernel/entry_64.S +0 -0

@@ -796,11 +793,22 @@ END(interrupt)
 
  /* 0(%rsp): ~(interrupt number) */

       .macro interrupt func
+       testl $3, CS-ORIG_RAX(%rsp)
+       je 1f
+       SWAPGS
+1:     btrl $0, PER_CPU_VAR(x86_irq_enable)
+       jc 2f
+       pushq $\func
+       CFI_ADJUST_CFA_OFFSET 8
+       jmp mark_irq_pending
+2:     TRACE_IRQS_OFF
       subq $10*8, %rsp
       CFI_ADJUST_CFA_OFFSET 10*8
       call save_args
       PARTIAL_FRAME 0
       call \func
+       TRACE_IRQS_ON
+       movl $1, PER_CPU_VAR(x86_irq_enable)
       .endm

 /*

arch/x86/kernel/entry_64.S +0 -0

@@ -818,8 +826,6 @@ common_interrupt:

       interrupt do_IRQ
       /* 0(%rsp): old_rsp-ARGOFFSET */
 ret_from_intr:
-       DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
       decl PER_CPU_VAR(irq_count)
       leaveq
       CFI_DEF_CFA_REGISTER    rsp

arch/x86/kernel/entry_64.S +0 -0

@@ -844,21 +850,8 @@ retint_check:

       jnz  retint_careful

 retint_swapgs:         /* return to user-space */
-       /*
-        * The iretq could re-enable interrupts:
-        */
-       DISABLE_INTERRUPTS(CLBR_ANY)
-       TRACE_IRQS_IRETQ
       SWAPGS
-       jmp restore_args
-
 retint_restore_args:   /* return to kernel space */
-       DISABLE_INTERRUPTS(CLBR_ANY)
-       /*
-        * The iretq could re-enable interrupts:
-        */
-       TRACE_IRQS_IRETQ
-restore_args:
       RESTORE_ARGS 0,8,0

 irq_return:

arch/x86/kernel/entry_64.S +0 -0

@@ -901,7 +894,7 @@ retint_careful:

       CFI_RESTORE_STATE
       bt    $TIF_NEED_RESCHED,%edx
       jnc   retint_signal
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       ENABLE_INTERRUPTS(CLBR_NONE)
       pushq %rdi
       CFI_ADJUST_CFA_OFFSET   8

arch/x86/kernel/entry_64.S +0 -0

@@ -910,13 +903,13 @@ retint_careful:

       CFI_ADJUST_CFA_OFFSET   -8
       GET_THREAD_INFO(%rcx)
       DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       jmp retint_check

 retint_signal:
       testl $_TIF_DO_NOTIFY_MASK,%edx
       jz    retint_swapgs
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       ENABLE_INTERRUPTS(CLBR_NONE)
       SAVE_REST
       movq $-1,ORIG_RAX(%rsp)

arch/x86/kernel/entry_64.S +0 -0

@@ -925,7 +918,7 @@ retint_signal:

       call do_notify_resume
       RESTORE_REST
       DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       GET_THREAD_INFO(%rcx)
       jmp retint_with_reschedule

arch/x86/kernel/entry_64.S +0 -0

@@ -937,14 +930,62 @@ ENTRY(retint_kernel)

       jnz  retint_restore_args
       bt  $TIF_NEED_RESCHED,TI_flags(%rcx)
       jnc  retint_restore_args
-       bt   $9,EFLAGS-ARGOFFSET(%rsp)  /* interrupts off? */
+       bt   $0, PER_CPU_VAR(x86_irq_enable)    /* interrupts off? */ jnc  retint_restore_args
+       bt   $9, EFLAGS-ARGOFFSET(%rsp)         /* hw interrupts off? */
+       jnc  retint_restore_args
+       movl $0, PER_CPU_VAR(x86_irq_enable)
+       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_ON
+       ENABLE_INTERRUPTS(CLBR_NONE)
       call preempt_schedule_irq
+       DISABLE_INTERRUPTS(CLBR_NONE)
+       TRACE_HW_IRQS_OFF
+       TRACE_IRQS_ON
+       movl $1, PER_CPU_VAR(x86_irq_enable)
       jmp exit_intr
 #endif

       CFI_ENDPROC
 END(common_interrupt)

arch/x86/kernel/entry_64.S +38 -0

+
+mark_irq_pending:
+       XCPT_FRAME 1 8
+       btl $31, PER_CPU_VAR(x86_irq_pending)   /* negative if pending */
+       jc 1f
+       popq PER_CPU_VAR(x86_irq_pending_handler)
+       CFI_ADJUST_CFA_OFFSET -8
+       popq PER_CPU_VAR(x86_irq_pending)
+       CFI_ADJUST_CFA_OFFSET -8
+       andl $~X86_EFLAGS_IF, EFLAGS-RIP(%rsp)
+       testl $3, CS-RIP(%rsp)
+       je irq_return
+       SWAPGS
+       jmp irq_return
+1:     ud2
+       CFI_ENDPROC
+
+/* void call_on_irq_stack(void *fn, void *arg) */
+ENTRY(call_on_irq_stack)
+       CFI_STARTPROC
+       pushq_cfi %rbp
+       CFI_REL_OFFSET rbp, 0
+       movq %rsp, %rbp
+       CFI_DEF_CFA_REGISTER %rbp
+       incl PER_CPU_VAR(irq_count)
+       cmove PER_CPU_VAR(irq_stack_ptr),%rsp
+       pushq %rbp                      # backlink for old unwinder
+       movq %rdi, %rcx
+       movq %rsi, %rdi
+       call *%rcx
+       leaveq
+       CFI_DEF_CFA_REGISTER %rsp
+       CFI_ADJUST_CFA_OFFSET -8
+       decl PER_CPU_VAR(irq_count)
+       ret
+       CFI_ENDPROC
+END(cal_irq_handler)
+

 /*
 * End of kprobes section
 */

arch/x86/kernel/entry_64.S +0 -0

@@ -1056,7 +1097,7 @@ ENTRY(\sym)

       CFI_ADJUST_CFA_OFFSET 8
       subq $15*8, %rsp
       call save_paranoid
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       movq %rsp,%rdi          /* pt_regs pointer */ xorl %esi,%esi          /* no error code */ call \do_sym

arch/x86/kernel/entry_64.S +0 -0

@@ -1073,7 +1114,7 @@ ENTRY(\sym)

       CFI_ADJUST_CFA_OFFSET 8
       subq $15*8, %rsp
       call save_paranoid
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       movq %rsp,%rdi          /* pt_regs pointer */ xorl %esi,%esi          /* no error code */ PER_CPU(init_tss, %r12)

arch/x86/kernel/entry_64.S +0 -0

@@ -1111,7 +1152,7 @@ ENTRY(\sym)

       CFI_ADJUST_CFA_OFFSET 15*8
       call save_paranoid
       DEFAULT_FRAME 0
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       movq %rsp,%rdi                  /* pt_regs pointer */ movq ORIG_RAX(%rsp),%rsi        /* get error code */ movq $-1,ORIG_RAX(%rsp)         /* no syscall to restart */

arch/x86/kernel/entry_64.S +0 -0

@@ -1367,18 +1408,18 @@ paranoidzeroentry machine_check *machine
  ENTRY(paranoid_exit)

       INTR_FRAME
       DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       testl %ebx,%ebx                         /* swapgs needed? */ jnz paranoid_restore
       testl $3,CS(%rsp)
       jnz   paranoid_userspace
 paranoid_swapgs:
-       TRACE_IRQS_IRETQ 0
+       TRACE_HW_IRQS_IRETQ 0
       SWAPGS_UNSAFE_STACK
       RESTORE_ALL 8
       jmp irq_return
 paranoid_restore:
-       TRACE_IRQS_IRETQ 0
+       TRACE_HW_IRQS_IRETQ 0
       RESTORE_ALL 8
       jmp irq_return
 paranoid_userspace:

arch/x86/kernel/entry_64.S +0 -0

@@ -1392,20 +1433,20 @@ paranoid_userspace:

       testl $_TIF_NEED_RESCHED,%ebx
       jnz paranoid_schedule
       movl %ebx,%edx                  /* arg3: thread flags */
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       ENABLE_INTERRUPTS(CLBR_NONE)
       xorl %esi,%esi                  /* arg2: oldset */ movq %rsp,%rdi                  /* arg1: &pt_regs */ call do_notify_resume DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       jmp paranoid_userspace
 paranoid_schedule:
-       TRACE_IRQS_ON
+       TRACE_HW_IRQS_ON
       ENABLE_INTERRUPTS(CLBR_ANY)
       call schedule
       DISABLE_INTERRUPTS(CLBR_ANY)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       jmp paranoid_userspace
       CFI_ENDPROC
 END(paranoid_exit)

arch/x86/kernel/entry_64.S +0 -0

@@ -1440,7 +1481,7 @@ ENTRY(error_entry)

 error_swapgs:
       SWAPGS
 error_sti:
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       ret
       CFI_ENDPROC

arch/x86/kernel/entry_64.S +0 -0

@@ -1476,7 +1517,7 @@ ENTRY(error_exit)

       movl %ebx,%eax
       RESTORE_REST
       DISABLE_INTERRUPTS(CLBR_NONE)
-       TRACE_IRQS_OFF
+       TRACE_HW_IRQS_OFF
       GET_THREAD_INFO(%rcx)
       testl %eax,%eax
       jne retint_kernel

arch/x86/kernel/entry_64.S +0 -0

@@ -1499,12 +1540,12 @@ ENTRY(nmi)

       CFI_ADJUST_CFA_OFFSET 15*8
       call save_paranoid
       DEFAULT_FRAME 0
-       /* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
+       /* paranoidentry do_nmi, 0; without TRACE_HW_IRQS_OFF */ movq %rsp,%rdi
       movq $-1,%rsi
       call do_nmi
 #ifdef CONFIG_TRACE_IRQFLAGS
-       /* paranoidexit; without TRACE_IRQS_OFF */
+       /* paranoidexit; without TRACE_HW_IRQS_OFF */
       /* ebx: no swapgs flag */ DISABLE_INTERRUPTS(CLBR_NONE)
       testl %ebx,%ebx                         /* swapgs needed? */
Index: work/arch/x86/kernel/process.c
===================================================================

arch/x86/kernel/process.c +0 -0

@@ -381,11 +381,10 @@ void default_idle(void)
 
                if (!need_resched())

                       safe_halt();    /* enables interrupts racelessly */
-               else
-                       local_irq_enable();
+               hw_irq_enable();
               current_thread_info()->status |= TS_POLLING;
       } else {
-               local_irq_enable();
+               hw_irq_enable();
               /* loop is done by the caller */
               cpu_relax();
       }

arch/x86/kernel/process.c +7 -9

@@ -396,7 +395,7 @@ EXPORT_SYMBOL(default_idle);
 
  void stop_this_cpu(void *dummy)
  {
-       local_irq_disable();
+       hw_irq_disable();
        /*
         * Remove this CPU:
         */

@@ -465,10 +464,8 @@ static void mwait_idle(void)
                smp_mb();
                if (!need_resched())
                        __sti_mwait(0, 0);
-               else
-                       local_irq_enable();
-       } else
-               local_irq_enable();
+       }
+       hw_irq_enable();
  }
 
  /*

@@ -479,7 +476,7 @@ static void mwait_idle(void)
  static void poll_idle(void)
  {
        trace_power_start(POWER_CSTATE, 0);
-       local_irq_enable();
+       hw_irq_enable();
        while (!need_resched())
                cpu_relax();
        trace_power_end(0);

@@ -614,9 +611,9 @@ static void c1e_idle(void)
                 * The switch back from broadcast mode needs to be
                 * called with interrupts disabled.
                 */
-                local_irq_disable();
-                clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
-                local_irq_enable();
+               hw_irq_disable();
+               clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT, &cpu);
+               hw_irq_enable();
        } else
                default_idle();
  }

Index: work/arch/x86/include/asm/irqflags.h
===================================================================

arch/x86/include/asm/irqflags.h +79 -24

@@ -4,6 +4,13 @@
  #include <asm/processor-flags.h>
 
  #ifndef __ASSEMBLY__
+
+#include <asm/percpu.h>
+
+DECLARE_PER_CPU(unsigned int, x86_irq_enable);         /* boolean switch */
+DECLARE_PER_CPU(unsigned long, x86_irq_pending);       /* pending vector */
+DECLARE_PER_CPU(void (*)(struct pt_regs *), x86_irq_pending_handler);
+
  /*
  * Interrupt control:
  */

@@ -54,6 +61,45 @@ static inline void native_halt(void)
        asm volatile("hlt": : :"memory");
  }
 
+extern void __raw_local_irq_enable_slow_path(void);
+
+static inline unsigned long __raw_local_save_flags(void)
+{
+       return percpu_read(x86_irq_enable);
+}
+
+static inline void raw_local_irq_restore(unsigned long flags)
+{
+       barrier();
+       percpu_write(x86_irq_enable, flags);
+       barrier();
+       if (flags && unlikely(percpu_read(x86_irq_pending)))
+               __raw_local_irq_enable_slow_path();
+}
+
+static inline void raw_local_irq_disable(void)
+{
+       percpu_write(x86_irq_enable, 0);
+       barrier();
+}
+
+static inline void raw_local_irq_enable(void)
+{
+       barrier();
+       percpu_write(x86_irq_enable, 1);
+       barrier();
+       if (unlikely(percpu_read(x86_irq_pending)))
+               __raw_local_irq_enable_slow_path();
+}
+
+static inline unsigned long __raw_local_irq_save(void)
+{
+       unsigned long flags = __raw_local_save_flags();
+
+       raw_local_irq_disable();
+
+       return flags;
+}
  #endif
 
  #ifdef CONFIG_PARAVIRT

@@ -61,22 +107,17 @@ static inline void native_halt(void)
  #else
  #ifndef __ASSEMBLY__
 
-static inline unsigned long __raw_local_save_flags(void)
+static inline unsigned long __raw_hw_save_flags(void)
  {
        return native_save_fl();
  }
 
-static inline void raw_local_irq_restore(unsigned long flags)
-{
-       native_restore_fl(flags);
-}
-
-static inline void raw_local_irq_disable(void)
+static inline void __raw_hw_irq_disable(void)
  {
        native_irq_disable();
  }
 
-static inline void raw_local_irq_enable(void)
+static inline void __raw_hw_irq_enable(void)
  {
        native_irq_enable();
  }

@@ -87,6 +128,7 @@ static inline void raw_local_irq_enable(
  */
  static inline void raw_safe_halt(void)
  {
+       percpu_write(x86_irq_enable, 1);
        native_safe_halt();
  }
 

@@ -99,17 +141,6 @@ static inline void halt(void)
        native_halt();
  }
 
-/*
- * For spinlocks, etc:
- */
-static inline unsigned long __raw_local_irq_save(void)
-{
-       unsigned long flags = __raw_local_save_flags();
-
-       raw_local_irq_disable();
-
-       return flags;
-}
  #else
 
  #define ENABLE_INTERRUPTS(x)   sti

@@ -161,14 +192,34 @@ static inline unsigned long __raw_local_
 
  static inline int raw_irqs_disabled_flags(unsigned long flags)
  {
-       return !(flags & X86_EFLAGS_IF);
+       return !flags;
  }
 
  static inline int raw_irqs_disabled(void)
  {
-       unsigned long flags = __raw_local_save_flags();
+       return raw_irqs_disabled_flags(__raw_local_save_flags());
+}
+
+#define __ARCH_HAS_HW_IRQ
+
+#define raw_hw_irq_save_flags(flags)                           \
+       do { (flags) = __raw_hw_save_flags(); } while (0)
+
+static inline void raw_hw_irq_disable(void)
+{
+       __raw_hw_irq_disable();
+       percpu_write(x86_irq_enable, 0);
+}
 
-       return raw_irqs_disabled_flags(flags);
+static inline void raw_hw_irq_enable(void)
+{
+       raw_local_irq_enable();
+       __raw_hw_irq_enable();
+}
+
+static inline int raw_hw_irqs_disabled_flags(unsigned long flags)
+{
+       return !(flags & X86_EFLAGS_IF);
  }
 
  #else

@@ -176,13 +227,13 @@ static inline int raw_irqs_disabled(void
  #ifdef CONFIG_X86_64
  #define ARCH_LOCKDEP_SYS_EXIT          call lockdep_sys_exit_thunk
  #define ARCH_LOCKDEP_SYS_EXIT_IRQ      \
-       TRACE_IRQS_ON; \
+       TRACE_HW_IRQS_ON; \
        sti; \
        SAVE_REST; \
        LOCKDEP_SYS_EXIT; \
        RESTORE_REST; \
        cli; \
-       TRACE_IRQS_OFF;
+       TRACE_HW_IRQS_OFF;
 
  #else
  #define ARCH_LOCKDEP_SYS_EXIT                  \

@@ -212,5 +263,9 @@ static inline int raw_irqs_disabled(void
  #  define LOCKDEP_SYS_EXIT_IRQ
  # endif
 
+/* HW IRQS tracing isn't implemented yet */
+#define TRACE_HW_IRQS_ON
+#define TRACE_HW_IRQS_OFF
+
  #endif /* __ASSEMBLY__ */
  #endif

Index: work/arch/x86/kernel/process_64.c
===================================================================

arch/x86/kernel/process_64.c +1 -1

@@ -132,7 +132,7 @@ void cpu_idle(void)
                         * from here on, until they go to idle.
                         * Otherwise, idle callbacks can misfire.
                         */
-                       local_irq_disable();
+                       hw_irq_disable();
                        enter_idle();
                        /* Don't trace irqs off for idle */
                        stop_critical_timings();

Index: work/arch/x86/kernel/smpboot.c
===================================================================

arch/x86/kernel/smpboot.c +1 -1

@@ -1364,7 +1364,7 @@ void play_dead_common(void)
        /*
         * With physical CPU hotplug, we should halt the cpu
         */
-       local_irq_disable();
+       hw_irq_disable();
  }
 
  void native_play_dead(void)

Index: work/arch/x86/include/asm/paravirt.h
===================================================================

arch/x86/include/asm/paravirt.h +4 -17

@@ -107,6 +107,7 @@ static inline void write_cr8(unsigned lo
 
  static inline void raw_safe_halt(void)
  {
+       percpu_write(x86_irq_enable, 1);
        PVOP_VCALL0(pv_irq_ops.safe_halt);
  }
 

@@ -829,35 +830,21 @@ static __always_inline void arch_spin_un
  #define __PV_IS_CALLEE_SAVE(func)                      \
        ((struct paravirt_callee_save) { func })
 
-static inline unsigned long __raw_local_save_flags(void)
+static inline unsigned long __raw_hw_save_flags(void)
  {
        return PVOP_CALLEE0(unsigned long, pv_irq_ops.save_fl);
  }
 
-static inline void raw_local_irq_restore(unsigned long f)
-{
-       PVOP_VCALLEE1(pv_irq_ops.restore_fl, f);
-}
-
-static inline void raw_local_irq_disable(void)
+static inline void __raw_hw_irq_disable(void)
  {
        PVOP_VCALLEE0(pv_irq_ops.irq_disable);
  }
 
-static inline void raw_local_irq_enable(void)
+static inline void __raw_hw_irq_enable(void)
  {
        PVOP_VCALLEE0(pv_irq_ops.irq_enable);
  }
 
-static inline unsigned long __raw_local_irq_save(void)
-{
-       unsigned long f;
-
-       f = __raw_local_save_flags();
-       raw_local_irq_disable();
-       return f;
-}
-
 
  /* Make sure as little as possible of this mess escapes. */
  #undef PARAVIRT_CALL

Index: work/arch/x86/kernel/irq.c
===================================================================

arch/x86/kernel/irq.c +21 -0

@@ -14,6 +14,7 @@
  #include <asm/idle.h>
  #include <asm/mce.h>
  #include <asm/hw_irq.h>
+#include <asm/desc.h>
 
  atomic_t irq_err_count;
 

@@ -217,6 +218,26 @@ u64 arch_irq_stat(void)
        return sum;
  }
 
+void call_on_irq_stack(void *fn, void *arg);
+
+void __raw_local_irq_enable_slow_path(void)
+{
+       struct pt_regs regs;
+
+       regs.sp = (unsigned long)&regs;
+       regs.orig_ax = percpu_read(x86_irq_pending);
+       regs.flags = 0x2;       /* bit 1 is always set */
+
+       percpu_write(x86_irq_enable, 0);
+       percpu_write(x86_irq_pending, 0);
+
+       call_on_irq_stack(percpu_read(x86_irq_pending_handler), &regs);
+
+       trace_hardirqs_on();
+       percpu_write(x86_irq_enable, 1);
+       __raw_hw_irq_enable();
+}
+EXPORT_SYMBOL(__raw_local_irq_enable_slow_path);
 
  /*
  * do_IRQ handles all normal device IRQ's (the special

Index: work/arch/x86/kernel/traps.c
===================================================================

arch/x86/kernel/traps.c +4 -4

@@ -86,26 +86,26 @@ static int ignore_nmis;
  static inline void conditional_sti(struct pt_regs *regs)
  {
        if (regs->flags & X86_EFLAGS_IF)
-               local_irq_enable();
+               __raw_hw_irq_enable();
  }
 
  static inline void preempt_conditional_sti(struct pt_regs *regs)
  {
        inc_preempt_count();
        if (regs->flags & X86_EFLAGS_IF)
-               local_irq_enable();
+               __raw_hw_irq_enable();
  }
 
  static inline void conditional_cli(struct pt_regs *regs)
  {
        if (regs->flags & X86_EFLAGS_IF)
-               local_irq_disable();
+               __raw_hw_irq_disable();
  }
 
  static inline void preempt_conditional_cli(struct pt_regs *regs)
  {
        if (regs->flags & X86_EFLAGS_IF)
-               local_irq_disable();
+               __raw_hw_irq_disable();
        dec_preempt_count();
  }
 

@@ -283,7 +283,7 @@ do_general_protection(struct pt_regs *re
 
  #ifdef CONFIG_X86_32

 gp_in_vm86:
-       local_irq_enable();
+       __raw_hw_irq_enable();
       handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code); return;
 #endif

arch/x86/kernel/traps.c +2 -2

@@ -749,7 +749,7 @@ asmlinkage void math_state_restore(void)
        struct task_struct *tsk = thread->task;
 
        if (!tsk_used_math(tsk)) {
-               local_irq_enable();
+               __raw_hw_irq_enable();
                /*
                 * does a slab alloc which can sleep
                 */

@@ -760,7 +760,7 @@ asmlinkage void math_state_restore(void)
                        do_group_exit(SIGKILL);
                        return;
                }
-               local_irq_disable();
+               __raw_hw_irq_disable();
        }
 

       clts();                         /* Allow maths ops (or we recurse) */

arch/x86/kernel/traps.c +1 -1

@@ -804,7 +804,7 @@ do_device_not_available(struct pt_regs *
  dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
  {
        siginfo_t info;
-       local_irq_enable();
+       __raw_hw_irq_enable();
 
        info.si_signo = SIGILL;
        info.si_errno = 0;

Index: work/arch/x86/mm/fault.c
===================================================================

arch/x86/mm/fault.c +3 -3

@@ -711,7 +711,7 @@ __bad_area_nosemaphore(struct pt_regs *r
                /*
                 * It's possible to have interrupts off here:
                 */
-               local_irq_enable();
+               __raw_hw_irq_enable();
 
                /*
                 * Valid to do another page fault here because this one came

@@ -1019,11 +1019,11 @@ do_page_fault(struct pt_regs *regs, unsi
         * potential system fault or CPU buglet:
         */
        if (user_mode_vm(regs)) {
-               local_irq_enable();
+               __raw_hw_irq_enable();
                error_code |= PF_USER;
        } else {
                if (regs->flags & X86_EFLAGS_IF)
-                       local_irq_enable();
+                       __raw_hw_irq_enable();
        }
 
        if (unlikely(error_code & PF_RSVD))

Index: work/lib/smp_processor_id.c
===================================================================

lib/smp_processor_id.c +1 -1

@@ -15,7 +15,7 @@ notrace unsigned int debug_smp_processor
        if (likely(preempt_count))
                goto out;
 
-       if (irqs_disabled())
+       if (hw_irqs_disabled())
                goto out;
 
        /*

But if it actually helps on real hardware (which is possible), that would be interesting. However, quite frankly, I doubt you can really measure it on any bigger load. cli-sti do not tend to be all that expensive any more (on a P4 it's probably noticeable, I doubt it shows up very much anywhere else).

I have seen some hits with cli-sti. I was considering swapping all preempt_disable() with local_irq_save() in ftrace, but hackbench showed a 30% performance degradation when I did that.

Quoted 6 lines · Tejun Heo

I just got it working and it behaves pretty good on qemu. Actual machines can't idle but seem to work otherwise. I'll fix up idle, get paravirt working and try to get some perf measurements but I'll be mostly off next week, so it will take some time. In the meantime, what do you guys think?

You need to show some real improvement on real hardware.

PS.  When did we start top-commenting and quoting the whole patch?

Quoted 4 lines · Steven Rostedt

I have seen some hits with cli-sti. I was considering swapping all preempt_disable() with local_irq_save() in ftrace, but hackbench showed a 30% performance degradation when I did that.

Yeah, but in that case you almost certainly keep the per-cpu cacheline hot in the D$ L1 cache, and the stack tracer is presumably also not taking any extra I$ L1 misses. So you're not seeing any of the downsides. The upside of plain cli/sti is that they're small, and have no D$ footprint.

And it's possible that the interrupt flag - at least if/when positioned right - wouldn't have any additional D$ footprint under normal load either. IOW, if there is an existing per-cpu cacheline that is effectively always already dirty and in the cache, But that's something that really needs macro-benchmarks - exactly because microbenchmarks don't show those effects since they are always basically hot-cache.

You need to show some real improvement on real hardware.

I can't really care less about qemu behavior. If the emulator is bad at emulating cli/sti, that's a qemu problem.

But if it actually helps on real hardware (which is possible), that would be interesting. However, quite frankly, I doubt you can really measure it on any bigger load. cli-sti do not tend to be all that expensive any more (on a P4 it's probably noticeable, I doubt it shows up very much anywhere else).

Quoted 4 lines · Steven Rostedt

I have seen some hits with cli-sti. I was considering swapping all preempt_disable() with local_irq_save() in ftrace, but hackbench showed a 30% performance degradation when I did that.

Yeah, but in that case you almost certainly keep the per-cpu cacheline hot in the D$ L1 cache, and the stack tracer is presumably also not taking any extra I$ L1 misses. So you're not seeing any of the downsides. The upside of plain cli/sti is that they're small, and have no D$ footprint.

And it's possible that the interrupt flag - at least if/when positioned right - wouldn't have any additional D$ footprint under normal load either. IOW, if there is an existing per-cpu cacheline that is effectively always already dirty and in the cache, But that's something that really needs macro-benchmarks - exactly because microbenchmarks don't show those effects since they are always basically hot-cache.

Also, the preempt code is pretty optimized and uses "add". Tejun uses "btrl" at least in some places, which is generally not a fast instruction. So there's a few caveats there too. Which is why I'd want numbers.

Also, is it worth trying to implement this soft disable generically? I know at least ppc64 does it today...

(Y'know, because your initial patch wasn't ambitious enough...)

Two changes are possible :

1) Get rid of the cpu_online_mask (its a const pointer to a known target). I cant see a reason for its need it actually...

2) Dont use a the last const qualifier but __read_mostly to move cpu_online_mask on same section.

Rusty, could you comment on one or other way before I submit a patch ?

(Of course, possible/present/active have same problem)

I'm not very convinced either. Nehalems are said to be able to do cli-sti sequences every 13 cycles or so, which sounds pretty good and managing it asynchronously might not buy anything. But what they said was cli-sti bandwidth, probably meaning that if you do cli-sti's in succession or tight loop, each iteration will take 13 cycles. So, there still could be cost related to instruction scheduling.

It only took me a couple of days to get it working and the changes are pretty localized, so I think it's worthwhile to see whether it actually helps anything on x86. I'm thinking about doing raw IOs on SSDs which isn't too unrealistic and heavy on both IRQ masking and IRQ handling although actual hardware access cost might just drown any difference and workloads which are heavy on memory allocations and such might be better fit. If you have any better ideas on testing, please let me know.

Hello,

This is something suggested by Rusty Russell a while ago. It makes IRQ masking a software switch like preemption or softirq enable/disable. Hardware interrupt masking (cli/sti) and delivery are decoupled from actual IRQ handling. IRQ disabling is done by single instruction moving 1 to a percpu variable. Enabling is similar but it should check whether there's any pending interrupt to handle.

This change greatly reduces the number of hardware IRQ masking manipulations. cli/sti still being somewhat costly operations (I hear nehalem is better tho), this should be able to improve overall performance, especially on paravirts.

I just got it working and it behaves pretty good on qemu. Actual machines can't idle but seem to work otherwise. I'll fix up idle, get paravirt working and try to get some perf measurements but I'll be mostly off next week, so it will take some time. In the meantime, what do you guys think?

Thanks.

HIGHLY_EXPERIMENTAL_DONT_APPLY

---
  arch/x86/ia32/ia32entry.S       |   12 +--
  arch/x86/include/asm/irqflags.h |  103 ++++++++++++++++++++++------
  arch/x86/include/asm/paravirt.h |   21 +----
  arch/x86/include/asm/system.h   |    4 -
  arch/x86/kernel/cpu/common.c    |   10 ++
  arch/x86/kernel/entry_64.S      |  143 +++++++++++++++++++++++++---------------
  arch/x86/kernel/irq.c           |   21 +++++
  arch/x86/kernel/process.c       |   21 ++---
  arch/x86/kernel/process_64.c    |    2
  arch/x86/kernel/smpboot.c       |    2
  arch/x86/kernel/traps.c         |   16 ++--
  arch/x86/mm/fault.c             |    6 -
  drivers/acpi/processor_idle.c   |   24 +++---
  drivers/cpuidle/cpuidle.c       |    6 -
  include/linux/irqflags.h        |   31 ++++++++
  init/main.c                     |    2
  lib/smp_processor_id.c          |    2
  17 files changed, 283 insertions(+), 143 deletions(-)

Index: work/drivers/acpi/processor_idle.c
===================================================================

drivers/acpi/processor_idle.c +12 -12

@@ -137,7 +137,7 @@ static void acpi_safe_halt(void)
  	smp_mb();
  	if (!need_resched()) {
  		safe_halt();
-		local_irq_disable();
+		hw_irq_disable();
  	}
  	current_thread_info()->status |= TS_POLLING;
  }

@@ -826,11 +826,11 @@ static int acpi_idle_enter_c1(struct cpu
  	if (unlikely(!pr))
  		return 0;
 
-	local_irq_disable();
+	hw_irq_disable();
 
  	/* Do not access any ACPI IO ports in suspend path */
  	if (acpi_idle_suspend) {
-		local_irq_enable();
+		hw_irq_enable();
  		cpu_relax();
  		return 0;
  	}

@@ -841,7 +841,7 @@ static int acpi_idle_enter_c1(struct cpu
  	kt2 = ktime_get_real();
  	idle_time =  ktime_to_us(ktime_sub(kt2, kt1));
 
-	local_irq_enable();
+	hw_irq_enable();
  	cx->usage++;
  	lapic_timer_state_broadcast(pr, cx, 0);
 

@@ -870,7 +870,7 @@ static int acpi_idle_enter_simple(struct
  	if (acpi_idle_suspend)
  		return(acpi_idle_enter_c1(dev, state));
 
-	local_irq_disable();
+	hw_irq_disable();
 
  	if (cx->entry_method != ACPI_CSTATE_FFH) {
  		current_thread_info()->status&= ~TS_POLLING;

@@ -882,7 +882,7 @@ static int acpi_idle_enter_simple(struct
 
  		if (unlikely(need_resched())) {
  			current_thread_info()->status |= TS_POLLING;
-			local_irq_enable();
+			hw_irq_enable();
  			return 0;
  		}
  	}

@@ -908,7 +908,7 @@ static int acpi_idle_enter_simple(struct
  	/* Tell the scheduler how much we idled: */
  	sched_clock_idle_wakeup_event(idle_time_ns);
 
-	local_irq_enable();
+	hw_irq_enable();
  	if (cx->entry_method != ACPI_CSTATE_FFH)
  		current_thread_info()->status |= TS_POLLING;
 

@@ -952,14 +952,14 @@ static int acpi_idle_enter_bm(struct cpu
  			dev->last_state = dev->safe_state;
  			return dev->safe_state->enter(dev, dev->safe_state);
  		} else {
-			local_irq_disable();
+			hw_irq_disable();
  			acpi_safe_halt();
-			local_irq_enable();
+			hw_irq_enable();
  			return 0;
  		}
  	}
 
-	local_irq_disable();
+	hw_irq_disable();
 
  	if (cx->entry_method != ACPI_CSTATE_FFH) {
  		current_thread_info()->status&= ~TS_POLLING;

@@ -971,7 +971,7 @@ static int acpi_idle_enter_bm(struct cpu
 
  		if (unlikely(need_resched())) {
  			current_thread_info()->status |= TS_POLLING;
-			local_irq_enable();
+			hw_irq_enable();
  			return 0;
  		}
  	}

@@ -1025,7 +1025,7 @@ static int acpi_idle_enter_bm(struct cpu
  	/* Tell the scheduler how much we idled: */
  	sched_clock_idle_wakeup_event(idle_time_ns);
 
-	local_irq_enable();
+	hw_irq_enable();
  	if (cx->entry_method != ACPI_CSTATE_FFH)
  		current_thread_info()->status |= TS_POLLING;
 

Index: work/drivers/cpuidle/cpuidle.c
===================================================================

drivers/cpuidle/cpuidle.c +3 -3

@@ -61,7 +61,7 @@ static void cpuidle_idle_call(void)
  #if defined(CONFIG_ARCH_HAS_DEFAULT_IDLE)
  			default_idle();
  #else
-			local_irq_enable();
+			hw_irq_enable();
  #endif
  		return;
  	}

@@ -77,7 +77,7 @@ static void cpuidle_idle_call(void)
  	/* ask the governor for the next state */
  	next_state = cpuidle_curr_governor->select(dev);
  	if (need_resched()) {
-		local_irq_enable();
+		hw_irq_enable();
  		return;
  	}
 

@@ -229,7 +229,7 @@ static int poll_idle(struct cpuidle_devi
  	int ret;
 
  	t1 = ktime_get();
-	local_irq_enable();
+	hw_irq_enable();
  	while (!need_resched())
  		cpu_relax();
 

Index: work/include/linux/irqflags.h
===================================================================

include/linux/irqflags.h +31 -0

@@ -79,6 +79,17 @@
  			raw_local_irq_restore(flags);	\
  		}					\
  	} while (0)
+
+#ifndef __ARCH_HAS_HW_IRQ
+#define raw_hw_irq_enable()		raw_local_irq_enable()
+#define raw_hw_irq_disable()		raw_local_irq_disable()
+#endif
+
+#define hw_irq_enable() \
+	do { trace_hardirqs_on(); raw_hw_irq_enable(); } while (0)
+#define hw_irq_disable() \
+	do { raw_hw_irq_disable(); trace_hardirqs_off(); } while (0)
+
  #else /* !CONFIG_TRACE_IRQFLAGS_SUPPORT */
  /*
   * The local_irq_*() APIs are equal to the raw_local_irq*()

@@ -96,6 +107,10 @@
  		typecheck(unsigned long, flags);	\
  		local_irq_restore(flags);		\
  	} while (0)
+# define raw_hw_irq_enable()		raw_local_irq_enable()
+# define raw_hw_irq_disable()		raw_local_irq_disable()
+# define hw_irq_enable()		raw_hw_irq_enable()
+# define hw_irq_disable()		raw_hw_irq_disable()
  #endif /* CONFIG_TRACE_IRQFLAGS_SUPPORT */
 
  #ifdef CONFIG_TRACE_IRQFLAGS_SUPPORT

@@ -124,6 +139,22 @@
  	typecheck(unsigned long, flags);	\
  	raw_irqs_disabled_flags(flags);		\
  })
+
+#ifdef __ARCH_HAS_HW_IRQ
+static inline bool hw_irqs_disabled(void)
+{
+	unsigned long flags;
+
+	if (irqs_disabled())
+		return true;
+
+	raw_hw_irq_save_flags(flags);
+	return raw_hw_irqs_disabled_flags(flags);
+}
+#else	/* __ARCH_HAS_HW_IRQ */
+#define hw_irqs_disabled()		irqs_disabled()
+#endif	/* __ARCH_HAS_HW_IRQ */
+
  #endif /* CONFIG_TRACE_IRQFLAGS_SUPPORT */
 
  #endif

Index: work/init/main.c
===================================================================

init/main.c +1 -1

@@ -626,7 +626,7 @@ asmlinkage void __init start_kernel(void
  		printk(KERN_CRIT "start_kernel(): bug: interrupts were "
  				 "enabled early\n");
  	early_boot_irqs_on();
-	local_irq_enable();
+	hw_irq_enable();
 
  	/* Interrupts are enabled now so all GFP allocations are safe. */
  	gfp_allowed_mask = __GFP_BITS_MASK;

Index: work/arch/x86/include/asm/system.h
===================================================================

arch/x86/include/asm/system.h +2 -2

@@ -102,8 +102,8 @@ do {									\
  #define __RESTORE(reg, offset) "movq (14-" #offset ")*8(%%rsp),%%" #reg "\n\t"
 
  /* frame pointer must be last for get_wchan */
-#define SAVE_CONTEXT    "pushf ; pushq %%rbp ; movq %%rsi,%%rbp\n\t"
-#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp ; popf\t"
+#define SAVE_CONTEXT    "pushq %%rbp ; movq %%rsi,%%rbp\n\t"
+#define RESTORE_CONTEXT "movq %%rbp,%%rsi ; popq %%rbp\t"
 
  #define __EXTRA_CLOBBER  \
  	, "rcx", "rbx", "rdx", "r8", "r9", "r10", "r11", \

Index: work/arch/x86/ia32/ia32entry.S
===================================================================

arch/x86/ia32/ia32entry.S +6 -6

@@ -162,7 +162,7 @@ sysenter_dispatch:
  	movq	%rax,RAX-ARGOFFSET(%rsp)
  	GET_THREAD_INFO(%r10)
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	testl	$_TIF_ALLWORK_MASK,TI_flags(%r10)
  	jnz	sysexit_audit
  sysexit_from_sys_call:

@@ -182,7 +182,7 @@ sysexit_from_sys_call:
  	popq	%rcx				/* User %esp */
  	CFI_ADJUST_CFA_OFFSET -8
  	CFI_REGISTER rsp,rcx
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	ENABLE_INTERRUPTS_SYSEXIT32
 
  #ifdef CONFIG_AUDITSYSCALL

@@ -207,7 +207,7 @@ sysexit_from_sys_call:
  	.macro auditsys_exit exit
  	testl $(_TIF_ALLWORK_MASK&  ~_TIF_SYSCALL_AUDIT),TI_flags(%r10)
  	jnz ia32_ret_from_sys_call
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	sti
  	movl %eax,%esi		/* second arg, syscall return value */
  	cmpl $0,%eax		/* is it<  0? */

@@ -219,7 +219,7 @@ sysexit_from_sys_call:
  	movl RAX-ARGOFFSET(%rsp),%eax	/* reload syscall return value */
  	movl $(_TIF_ALLWORK_MASK&  ~_TIF_SYSCALL_AUDIT),%edi
  	cli
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	testl %edi,TI_flags(%r10)
  	jz \exit
  	CLEAR_RREGS -ARGOFFSET

@@ -323,7 +323,7 @@ cstar_dispatch:
  	movq %rax,RAX-ARGOFFSET(%rsp)
  	GET_THREAD_INFO(%r10)
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	testl $_TIF_ALLWORK_MASK,TI_flags(%r10)
  	jnz sysretl_audit
  sysretl_from_sys_call:

@@ -336,7 +336,7 @@ sysretl_from_sys_call:
  	xorq	%r10,%r10
  	xorq	%r9,%r9
  	xorq	%r8,%r8
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	movl RSP-ARGOFFSET(%rsp),%esp
  	CFI_RESTORE rsp
  	USERGS_SYSRET32

Index: work/arch/x86/kernel/cpu/common.c
===================================================================

arch/x86/kernel/cpu/common.c +4 -1

+
+DEFINE_PER_CPU(void (*)(struct pt_regs *), x86_irq_pending_handler) = NULL;
+
  /*
   * Special IST stacks which the CPU switches to when it calls
   * an IST-marked descriptor entry. Up to 7 stacks (hardware

@@ -1211,7 +1219,7 @@ void __cpuinit cpu_init(void)
  	if (cpumask_test_and_set_cpu(cpu, cpu_initialized_mask)) {
  		printk(KERN_WARNING "CPU#%d already initialized!\n", cpu);
  		for (;;)
-			local_irq_enable();
+			hw_irq_enable();
  	}
 
  	printk(KERN_INFO "Initializing CPU#%d\n", cpu);

Index: work/arch/x86/kernel/entry_64.S
===================================================================

arch/x86/kernel/entry_64.S +14 -17

@@ -175,11 +175,11 @@ ENDPROC(native_usergs_sysret64)
  #endif /* CONFIG_PARAVIRT */
 
 
-.macro TRACE_IRQS_IRETQ offset=ARGOFFSET
+.macro TRACE_HW_IRQS_IRETQ offset=ARGOFFSET
  #ifdef CONFIG_TRACE_IRQFLAGS
  	bt   $9,EFLAGS-\offset(%rsp)	/* interrupts off? */
  	jnc  1f
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  1:
  #endif
  .endm

@@ -317,17 +317,14 @@ ENTRY(save_args)
  	leaq -ARGOFFSET+16(%rsp),%rdi	/* arg1 for handler */
  	movq_cfi rbp, 8		/* push %rbp */
  	leaq 8(%rsp), %rbp		/* mov %rsp, %ebp */
-	testl $3, CS(%rdi)
-	je 1f
-	SWAPGS
  	/*
  	 * irq_count is used to check if a CPU is already on an interrupt stack
  	 * or not. While this is essentially redundant with preempt_count it is
  	 * a little cheaper to use a separate counter in the PDA (short of
  	 * moving irq_enter into assembly, which would be too much work)
  	 */
-1:	incl PER_CPU_VAR(irq_count)
-	jne 2f
+	incl PER_CPU_VAR(irq_count)
+	jne 1f
  	popq_cfi %rax			/* move return address... */
  	mov PER_CPU_VAR(irq_stack_ptr),%rsp
  	EMPTY_FRAME 0

@@ -336,7 +333,7 @@ ENTRY(save_args)
  	/*
  	 * We entered an interrupt context - irqs are off:
  	 */
-2:	TRACE_IRQS_OFF
+1:	TRACE_HW_IRQS_OFF
  	ret
  	CFI_ENDPROC
  END(save_args)

@@ -497,7 +494,7 @@ sysret_check:
  	LOCKDEP_SYS_EXIT
  	GET_THREAD_INFO(%rcx)
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	movl TI_flags(%rcx),%edx
  	andl %edi,%edx
  	jnz  sysret_careful

@@ -505,7 +502,7 @@ sysret_check:
  	/*
  	 * sysretq will re-enable interrupts:
  	 */
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	movq RIP-ARGOFFSET(%rsp),%rcx
  	CFI_REGISTER	rip,rcx
  	RESTORE_ARGS 0,-ARG_SKIP,1

@@ -519,7 +516,7 @@ sysret_check:
  sysret_careful:
  	bt $TIF_NEED_RESCHED,%edx
  	jnc sysret_signal
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	ENABLE_INTERRUPTS(CLBR_NONE)
  	pushq %rdi
  	CFI_ADJUST_CFA_OFFSET 8

@@ -530,7 +527,7 @@ sysret_careful:
 
  	/* Handle a signal */
  sysret_signal:
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	ENABLE_INTERRUPTS(CLBR_NONE)
  #ifdef CONFIG_AUDITSYSCALL
  	bt $TIF_SYSCALL_AUDIT,%edx

@@ -612,7 +609,7 @@ tracesys:
   */
  GLOBAL(int_ret_from_sys_call)
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	testl $3,CS-ARGOFFSET(%rsp)
  	je retint_restore_args
  	movl $_TIF_ALLWORK_MASK,%edi

@@ -632,7 +629,7 @@ GLOBAL(int_with_check)
  int_careful:
  	bt $TIF_NEED_RESCHED,%edx
  	jnc  int_very_careful
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	ENABLE_INTERRUPTS(CLBR_NONE)
  	pushq %rdi
  	CFI_ADJUST_CFA_OFFSET 8

@@ -640,12 +637,12 @@ int_careful:
  	popq %rdi
  	CFI_ADJUST_CFA_OFFSET -8
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	jmp int_with_check
 
  	/* handle signals and tracing -- both require a full stack frame */
  int_very_careful:
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	ENABLE_INTERRUPTS(CLBR_NONE)
  int_check_syscall_exit_work:
  	SAVE_REST

@@ -671,7 +668,7 @@ int_signal:
  int_restore_rest:
  	RESTORE_REST
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	jmp int_with_check
  	CFI_ENDPROC
  END(system_call)

arch/x86/kernel/entry_64.S +67 -34

  	.endm
 
  /*

@@ -818,8 +826,6 @@ common_interrupt:
  	interrupt do_IRQ
  	/* 0(%rsp): old_rsp-ARGOFFSET */
  ret_from_intr:
-	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
  	decl PER_CPU_VAR(irq_count)
  	leaveq
  	CFI_DEF_CFA_REGISTER	rsp

@@ -844,21 +850,8 @@ retint_check:
  	jnz  retint_careful
 
  retint_swapgs:		/* return to user-space */
-	/*
-	 * The iretq could re-enable interrupts:
-	 */
-	DISABLE_INTERRUPTS(CLBR_ANY)
-	TRACE_IRQS_IRETQ
  	SWAPGS
-	jmp restore_args
-
  retint_restore_args:	/* return to kernel space */
-	DISABLE_INTERRUPTS(CLBR_ANY)
-	/*
-	 * The iretq could re-enable interrupts:
-	 */
-	TRACE_IRQS_IRETQ
-restore_args:
  	RESTORE_ARGS 0,8,0
 
  irq_return:

@@ -901,7 +894,7 @@ retint_careful:
  	CFI_RESTORE_STATE
  	bt    $TIF_NEED_RESCHED,%edx
  	jnc   retint_signal
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	ENABLE_INTERRUPTS(CLBR_NONE)
  	pushq %rdi
  	CFI_ADJUST_CFA_OFFSET	8

@@ -910,13 +903,13 @@ retint_careful:
  	CFI_ADJUST_CFA_OFFSET	-8
  	GET_THREAD_INFO(%rcx)
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	jmp retint_check
 
  retint_signal:
  	testl $_TIF_DO_NOTIFY_MASK,%edx
  	jz    retint_swapgs
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	ENABLE_INTERRUPTS(CLBR_NONE)
  	SAVE_REST
  	movq $-1,ORIG_RAX(%rsp)

@@ -925,7 +918,7 @@ retint_signal:
  	call do_notify_resume
  	RESTORE_REST
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	GET_THREAD_INFO(%rcx)
  	jmp retint_with_reschedule
 

@@ -937,14 +930,62 @@ ENTRY(retint_kernel)
  	jnz  retint_restore_args
  	bt  $TIF_NEED_RESCHED,TI_flags(%rcx)
  	jnc  retint_restore_args
-	bt   $9,EFLAGS-ARGOFFSET(%rsp)	/* interrupts off? */
+	bt   $0, PER_CPU_VAR(x86_irq_enable)	/* interrupts off? */
  	jnc  retint_restore_args
+	bt   $9, EFLAGS-ARGOFFSET(%rsp)		/* hw interrupts off? */
+	jnc  retint_restore_args
+	movl $0, PER_CPU_VAR(x86_irq_enable)
+	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_ON
+	ENABLE_INTERRUPTS(CLBR_NONE)
  	call preempt_schedule_irq
+	DISABLE_INTERRUPTS(CLBR_NONE)
+	TRACE_HW_IRQS_OFF
+	TRACE_IRQS_ON
+	movl $1, PER_CPU_VAR(x86_irq_enable)
  	jmp exit_intr
  #endif
 
  	CFI_ENDPROC
  END(common_interrupt)
+
+mark_irq_pending:
+	XCPT_FRAME 1 8
+	btl $31, PER_CPU_VAR(x86_irq_pending)	/* negative if pending */
+	jc 1f
+	popq PER_CPU_VAR(x86_irq_pending_handler)
+	CFI_ADJUST_CFA_OFFSET -8
+	popq PER_CPU_VAR(x86_irq_pending)
+	CFI_ADJUST_CFA_OFFSET -8
+	andl $~X86_EFLAGS_IF, EFLAGS-RIP(%rsp)
+	testl $3, CS-RIP(%rsp)
+	je irq_return
+	SWAPGS
+	jmp irq_return
+1:	ud2
+	CFI_ENDPROC
+
+/* void call_on_irq_stack(void *fn, void *arg) */
+ENTRY(call_on_irq_stack)
+	CFI_STARTPROC
+	pushq_cfi %rbp
+	CFI_REL_OFFSET rbp, 0
+	movq %rsp, %rbp
+	CFI_DEF_CFA_REGISTER %rbp
+	incl PER_CPU_VAR(irq_count)
+	cmove PER_CPU_VAR(irq_stack_ptr),%rsp
+	pushq %rbp			# backlink for old unwinder
+	movq %rdi, %rcx
+	movq %rsi, %rdi
+	call *%rcx
+	leaveq
+	CFI_DEF_CFA_REGISTER %rsp
+	CFI_ADJUST_CFA_OFFSET -8
+	decl PER_CPU_VAR(irq_count)
+	ret
+	CFI_ENDPROC
+END(cal_irq_handler)
+
  /*
   * End of kprobes section
   */

@@ -1056,7 +1097,7 @@ ENTRY(\sym)
  	CFI_ADJUST_CFA_OFFSET 8
  	subq $15*8, %rsp
  	call save_paranoid
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	movq %rsp,%rdi		/* pt_regs pointer */
  	xorl %esi,%esi		/* no error code */
  	call \do_sym

@@ -1073,7 +1114,7 @@ ENTRY(\sym)
  	CFI_ADJUST_CFA_OFFSET 8
  	subq $15*8, %rsp
  	call save_paranoid
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	movq %rsp,%rdi		/* pt_regs pointer */
  	xorl %esi,%esi		/* no error code */
  	PER_CPU(init_tss, %r12)

@@ -1111,7 +1152,7 @@ ENTRY(\sym)
  	CFI_ADJUST_CFA_OFFSET 15*8
  	call save_paranoid
  	DEFAULT_FRAME 0
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	movq %rsp,%rdi			/* pt_regs pointer */
  	movq ORIG_RAX(%rsp),%rsi	/* get error code */
  	movq $-1,ORIG_RAX(%rsp)		/* no syscall to restart */

@@ -1367,18 +1408,18 @@ paranoidzeroentry machine_check *machine
  ENTRY(paranoid_exit)
  	INTR_FRAME
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	testl %ebx,%ebx				/* swapgs needed? */
  	jnz paranoid_restore
  	testl $3,CS(%rsp)
  	jnz   paranoid_userspace
  paranoid_swapgs:
-	TRACE_IRQS_IRETQ 0
+	TRACE_HW_IRQS_IRETQ 0
  	SWAPGS_UNSAFE_STACK
  	RESTORE_ALL 8
  	jmp irq_return
  paranoid_restore:
-	TRACE_IRQS_IRETQ 0
+	TRACE_HW_IRQS_IRETQ 0
  	RESTORE_ALL 8
  	jmp irq_return
  paranoid_userspace:

@@ -1392,20 +1433,20 @@ paranoid_userspace:
  	testl $_TIF_NEED_RESCHED,%ebx
  	jnz paranoid_schedule
  	movl %ebx,%edx			/* arg3: thread flags */
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	ENABLE_INTERRUPTS(CLBR_NONE)
  	xorl %esi,%esi 			/* arg2: oldset */
  	movq %rsp,%rdi 			/* arg1:&pt_regs */
  	call do_notify_resume
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	jmp paranoid_userspace
  paranoid_schedule:
-	TRACE_IRQS_ON
+	TRACE_HW_IRQS_ON
  	ENABLE_INTERRUPTS(CLBR_ANY)
  	call schedule
  	DISABLE_INTERRUPTS(CLBR_ANY)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	jmp paranoid_userspace
  	CFI_ENDPROC
  END(paranoid_exit)

@@ -1440,7 +1481,7 @@ ENTRY(error_entry)
  error_swapgs:
  	SWAPGS
  error_sti:
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	ret
  	CFI_ENDPROC
 

@@ -1476,7 +1517,7 @@ ENTRY(error_exit)
  	movl %ebx,%eax
  	RESTORE_REST
  	DISABLE_INTERRUPTS(CLBR_NONE)
-	TRACE_IRQS_OFF
+	TRACE_HW_IRQS_OFF
  	GET_THREAD_INFO(%rcx)
  	testl %eax,%eax
  	jne retint_kernel

@@ -1499,12 +1540,12 @@ ENTRY(nmi)
  	CFI_ADJUST_CFA_OFFSET 15*8
  	call save_paranoid
  	DEFAULT_FRAME 0
-	/* paranoidentry do_nmi, 0; without TRACE_IRQS_OFF */
+	/* paranoidentry do_nmi, 0; without TRACE_HW_IRQS_OFF */
  	movq %rsp,%rdi
  	movq $-1,%rsi
  	call do_nmi
  #ifdef CONFIG_TRACE_IRQFLAGS
-	/* paranoidexit; without TRACE_IRQS_OFF */
+	/* paranoidexit; without TRACE_HW_IRQS_OFF */
  	/* ebx:	no swapgs flag */
  	DISABLE_INTERRUPTS(CLBR_NONE)
  	testl %ebx,%ebx				/* swapgs needed? */

Index: work/arch/x86/kernel/process.c
===================================================================

arch/x86/kernel/process.c +9 -12

@@ -381,11 +381,10 @@ void default_idle(void)
 
  		if (!need_resched())
  			safe_halt();	/* enables interrupts racelessly */
-		else
-			local_irq_enable();
+		hw_irq_enable();
  		current_thread_info()->status |= TS_POLLING;
  	} else {
-		local_irq_enable();
+		hw_irq_enable();
  		/* loop is done by the caller */
  		cpu_relax();
  	}

@@ -396,7 +395,7 @@ EXPORT_SYMBOL(default_idle);
 
  void stop_this_cpu(void *dummy)
  {
-	local_irq_disable();
+	hw_irq_disable();
  	/*
  	 * Remove this CPU:
  	 */

@@ -465,10 +464,8 @@ static void mwait_idle(void)
  		smp_mb();
  		if (!need_resched())
  			__sti_mwait(0, 0);
-		else
-			local_irq_enable();
-	} else
-		local_irq_enable();
+	}
+	hw_irq_enable();
  }
 
  /*

@@ -479,7 +476,7 @@ static void mwait_idle(void)
  static void poll_idle(void)
  {
  	trace_power_start(POWER_CSTATE, 0);
-	local_irq_enable();
+	hw_irq_enable();
  	while (!need_resched())
  		cpu_relax();
  	trace_power_end(0);

@@ -614,9 +611,9 @@ static void c1e_idle(void)
  		 * The switch back from broadcast mode needs to be
  		 * called with interrupts disabled.
  		 */
-		 local_irq_disable();
-		 clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT,&cpu);
-		 local_irq_enable();
+		hw_irq_disable();
+		clockevents_notify(CLOCK_EVT_NOTIFY_BROADCAST_EXIT,&cpu);
+		hw_irq_enable();
  	} else
  		default_idle();
  }

Index: work/arch/x86/include/asm/irqflags.h
===================================================================

arch/x86/include/asm/irqflags.h +79 -24

@@ -4,6 +4,13 @@
  #include<asm/processor-flags.h>
 
  #ifndef __ASSEMBLY__
+
+#include<asm/percpu.h>
+
+DECLARE_PER_CPU(unsigned int, x86_irq_enable);		/* boolean switch */
+DECLARE_PER_CPU(unsigned long, x86_irq_pending);	/* pending vector */
+DECLARE_PER_CPU(void (*)(struct pt_regs *), x86_irq_pending_handler);
+
  /*
   * Interrupt control:
   */

@@ -54,6 +61,45 @@ static inline void native_halt(void)
  	asm volatile("hlt": : :"memory");
  }
 
+extern void __raw_local_irq_enable_slow_path(void);
+
+static inline unsigned long __raw_local_save_flags(void)
+{
+	return percpu_read(x86_irq_enable);
+}
+
+static inline void raw_local_irq_restore(unsigned long flags)
+{
+	barrier();
+	percpu_write(x86_irq_enable, flags);
+	barrier();
+	if (flags&&  unlikely(percpu_read(x86_irq_pending)))
+		__raw_local_irq_enable_slow_path();
+}
+
+static inline void raw_local_irq_disable(void)
+{
+	percpu_write(x86_irq_enable, 0);
+	barrier();
+}
+
+static inline void raw_local_irq_enable(void)
+{
+	barrier();
+	percpu_write(x86_irq_enable, 1);
+	barrier();
+	if (unlikely(percpu_read(x86_irq_pending)))
+		__raw_local_irq_enable_slow_path();
+}
+
+static inline unsigned long __raw_local_irq_save(void)
+{
+	unsigned long flags = __raw_local_save_flags();
+
+	raw_local_irq_disable();
+
+	return flags;
+}
  #endif
 
  #ifdef CONFIG_PARAVIRT

@@ -61,22 +107,17 @@ static inline void native_halt(void)
  #else
  #ifndef __ASSEMBLY__
 
-static inline unsigned long __raw_local_save_flags(void)
+static inline unsigned long __raw_hw_save_flags(void)
  {
  	return native_save_fl();
  }
 
-static inline void raw_local_irq_restore(unsigned long flags)
-{
-	native_restore_fl(flags);
-}
-
-static inline void raw_local_irq_disable(void)
+static inline void __raw_hw_irq_disable(void)
  {
  	native_irq_disable();
  }
 
-static inline void raw_local_irq_enable(void)
+static inline void __raw_hw_irq_enable(void)
  {
  	native_irq_enable();
  }

@@ -87,6 +128,7 @@ static inline void raw_local_irq_enable(
   */
  static inline void raw_safe_halt(void)
  {
+	percpu_write(x86_irq_enable, 1);
  	native_safe_halt();
  }
 

@@ -99,17 +141,6 @@ static inline void halt(void)
  	native_halt();
  }
 
-/*
- * For spinlocks, etc:
- */
-static inline unsigned long __raw_local_irq_save(void)
-{
-	unsigned long flags = __raw_local_save_flags();
-
-	raw_local_irq_disable();
-
-	return flags;
-}
  #else
 
  #define ENABLE_INTERRUPTS(x)	sti

@@ -161,14 +192,34 @@ static inline unsigned long __raw_local_
 
  static inline int raw_irqs_disabled_flags(unsigned long flags)
  {
-	return !(flags&  X86_EFLAGS_IF);
+	return !flags;
  }
 
  static inline int raw_irqs_disabled(void)
  {
-	unsigned long flags = __raw_local_save_flags();
+	return raw_irqs_disabled_flags(__raw_local_save_flags());
+}
+
+#define __ARCH_HAS_HW_IRQ
+
+#define raw_hw_irq_save_flags(flags)				\
+	do { (flags) = __raw_hw_save_flags(); } while (0)
+
+static inline void raw_hw_irq_disable(void)
+{
+	__raw_hw_irq_disable();
+	percpu_write(x86_irq_enable, 0);
+}
 
-	return raw_irqs_disabled_flags(flags);
+static inline void raw_hw_irq_enable(void)
+{
+	raw_local_irq_enable();
+	__raw_hw_irq_enable();
+}
+
+static inline int raw_hw_irqs_disabled_flags(unsigned long flags)
+{
+	return !(flags&  X86_EFLAGS_IF);
  }
 
  #else

@@ -176,13 +227,13 @@ static inline int raw_irqs_disabled(void
  #ifdef CONFIG_X86_64
  #define ARCH_LOCKDEP_SYS_EXIT		call lockdep_sys_exit_thunk
  #define ARCH_LOCKDEP_SYS_EXIT_IRQ	\
-	TRACE_IRQS_ON; \
+	TRACE_HW_IRQS_ON; \
  	sti; \
  	SAVE_REST; \
  	LOCKDEP_SYS_EXIT; \
  	RESTORE_REST; \
  	cli; \
-	TRACE_IRQS_OFF;
+	TRACE_HW_IRQS_OFF;
 
  #else
  #define ARCH_LOCKDEP_SYS_EXIT			\

@@ -212,5 +263,9 @@ static inline int raw_irqs_disabled(void
  #  define LOCKDEP_SYS_EXIT_IRQ
  # endif
 
+/* HW IRQS tracing isn't implemented yet */
+#define TRACE_HW_IRQS_ON
+#define TRACE_HW_IRQS_OFF
+
  #endif /* __ASSEMBLY__ */
  #endif

Index: work/arch/x86/kernel/process_64.c
===================================================================

arch/x86/kernel/process_64.c +1 -1

@@ -132,7 +132,7 @@ void cpu_idle(void)
  			 * from here on, until they go to idle.
  			 * Otherwise, idle callbacks can misfire.
  			 */
-			local_irq_disable();
+			hw_irq_disable();
  			enter_idle();
  			/* Don't trace irqs off for idle */
  			stop_critical_timings();

Index: work/arch/x86/kernel/smpboot.c
===================================================================

arch/x86/kernel/smpboot.c +1 -1

@@ -1364,7 +1364,7 @@ void play_dead_common(void)
  	/*
  	 * With physical CPU hotplug, we should halt the cpu
  	 */
-	local_irq_disable();
+	hw_irq_disable();
  }
 
  void native_play_dead(void)

Index: work/arch/x86/include/asm/paravirt.h
===================================================================

arch/x86/include/asm/paravirt.h +4 -17

@@ -107,6 +107,7 @@ static inline void write_cr8(unsigned lo
 
  static inline void raw_safe_halt(void)
  {
+	percpu_write(x86_irq_enable, 1);
  	PVOP_VCALL0(pv_irq_ops.safe_halt);
  }
 

@@ -829,35 +830,21 @@ static __always_inline void arch_spin_un
  #define __PV_IS_CALLEE_SAVE(func)			\
  	((struct paravirt_callee_save) { func })
 
-static inline unsigned long __raw_local_save_flags(void)
+static inline unsigned long __raw_hw_save_flags(void)
  {
  	return PVOP_CALLEE0(unsigned long, pv_irq_ops.save_fl);
  }
 
-static inline void raw_local_irq_restore(unsigned long f)
-{
-	PVOP_VCALLEE1(pv_irq_ops.restore_fl, f);
-}
-
-static inline void raw_local_irq_disable(void)
+static inline void __raw_hw_irq_disable(void)
  {
  	PVOP_VCALLEE0(pv_irq_ops.irq_disable);
  }
 
-static inline void raw_local_irq_enable(void)
+static inline void __raw_hw_irq_enable(void)
  {
  	PVOP_VCALLEE0(pv_irq_ops.irq_enable);
  }
 
-static inline unsigned long __raw_local_irq_save(void)
-{
-	unsigned long f;
-
-	f = __raw_local_save_flags();
-	raw_local_irq_disable();
-	return f;
-}
-
 
  /* Make sure as little as possible of this mess escapes. */
  #undef PARAVIRT_CALL

Index: work/arch/x86/kernel/irq.c
===================================================================

arch/x86/kernel/irq.c +21 -0

@@ -14,6 +14,7 @@
  #include<asm/idle.h>
  #include<asm/mce.h>
  #include<asm/hw_irq.h>
+#include<asm/desc.h>
 
  atomic_t irq_err_count;
 

@@ -217,6 +218,26 @@ u64 arch_irq_stat(void)
  	return sum;
  }
 
+void call_on_irq_stack(void *fn, void *arg);
+
+void __raw_local_irq_enable_slow_path(void)
+{
+	struct pt_regs regs;
+
+	regs.sp = (unsigned long)&regs;
+	regs.orig_ax = percpu_read(x86_irq_pending);
+	regs.flags = 0x2;	/* bit 1 is always set */
+
+	percpu_write(x86_irq_enable, 0);
+	percpu_write(x86_irq_pending, 0);
+
+	call_on_irq_stack(percpu_read(x86_irq_pending_handler),&regs);
+
+	trace_hardirqs_on();
+	percpu_write(x86_irq_enable, 1);
+	__raw_hw_irq_enable();
+}
+EXPORT_SYMBOL(__raw_local_irq_enable_slow_path);
 
  /*
   * do_IRQ handles all normal device IRQ's (the special

Index: work/arch/x86/kernel/traps.c
===================================================================

arch/x86/kernel/traps.c +8 -8

@@ -86,26 +86,26 @@ static int ignore_nmis;
  static inline void conditional_sti(struct pt_regs *regs)
  {
  	if (regs->flags&  X86_EFLAGS_IF)
-		local_irq_enable();
+		__raw_hw_irq_enable();
  }
 
  static inline void preempt_conditional_sti(struct pt_regs *regs)
  {
  	inc_preempt_count();
  	if (regs->flags&  X86_EFLAGS_IF)
-		local_irq_enable();
+		__raw_hw_irq_enable();
  }
 
  static inline void conditional_cli(struct pt_regs *regs)
  {
  	if (regs->flags&  X86_EFLAGS_IF)
-		local_irq_disable();
+		__raw_hw_irq_disable();
  }
 
  static inline void preempt_conditional_cli(struct pt_regs *regs)
  {
  	if (regs->flags&  X86_EFLAGS_IF)
-		local_irq_disable();
+		__raw_hw_irq_disable();
  	dec_preempt_count();
  }
 

@@ -283,7 +283,7 @@ do_general_protection(struct pt_regs *re
 
  #ifdef CONFIG_X86_32
  gp_in_vm86:
-	local_irq_enable();
+	__raw_hw_irq_enable();
  	handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
  	return;
  #endif

@@ -749,7 +749,7 @@ asmlinkage void math_state_restore(void)
  	struct task_struct *tsk = thread->task;
 
  	if (!tsk_used_math(tsk)) {
-		local_irq_enable();
+		__raw_hw_irq_enable();
  		/*
  		 * does a slab alloc which can sleep
  		 */

@@ -760,7 +760,7 @@ asmlinkage void math_state_restore(void)
  			do_group_exit(SIGKILL);
  			return;
  		}
-		local_irq_disable();
+		__raw_hw_irq_disable();
  	}
 
  	clts();				/* Allow maths ops (or we recurse) */

@@ -804,7 +804,7 @@ do_device_not_available(struct pt_regs *
  dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
  {
  	siginfo_t info;
-	local_irq_enable();
+	__raw_hw_irq_enable();
 
  	info.si_signo = SIGILL;
  	info.si_errno = 0;

Index: work/arch/x86/mm/fault.c
===================================================================

arch/x86/mm/fault.c +3 -3

@@ -711,7 +711,7 @@ __bad_area_nosemaphore(struct pt_regs *r
  		/*
  		 * It's possible to have interrupts off here:
  		 */
-		local_irq_enable();
+		__raw_hw_irq_enable();
 
  		/*
  		 * Valid to do another page fault here because this one came

@@ -1019,11 +1019,11 @@ do_page_fault(struct pt_regs *regs, unsi
  	 * potential system fault or CPU buglet:
  	 */
  	if (user_mode_vm(regs)) {
-		local_irq_enable();
+		__raw_hw_irq_enable();
  		error_code |= PF_USER;
  	} else {
  		if (regs->flags&  X86_EFLAGS_IF)
-			local_irq_enable();
+			__raw_hw_irq_enable();
  	}
 
  	if (unlikely(error_code&  PF_RSVD))

Index: work/lib/smp_processor_id.c
===================================================================

lib/smp_processor_id.c +1 -2

@@ -15,7 +15,7 @@ notrace unsigned int debug_smp_processor
  	if (likely(preempt_count))
  		goto out;
 
-	if (irqs_disabled())
+	if (hw_irqs_disabled())
  		goto out;
 
  	/*
--

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Of course if it becomes core to the x86 architecture or the kernel overall, then most of the irq-related paravirt-ops can go away and be limited to the actual interrupt handler and the machinery needed to really mask/unmask the hardware and set the pending flag (which would likely just be contained within the hypervisor-specific code, and not need any new kernel interfaces to replace the dropped paravirt irq ones).