making SLUB -rt friendly

kernel/workqueue.c int fastcall queue_work(struct workqueue · line 189

Quoted 12 lines · Peter Zijlstra

kernel/workqueue.c +11 -0

+int fastcall queue_work_cpu(struct workqueue_struct *wq, struct work_struct *work, int cpu)
+{
+	int ret = 0;
+
+	if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
+		BUG_ON(!list_empty(&work->entry));
+		__queue_work(wq_per_cpu(wq, cpu), work);
+		ret = 1;
+	}
+	return ret;
+}

Minor nit, we already have queue_delayed_work_on(), perhaps it should be named queue_work_on().

From: Mathieu Desnoyers <[email protected]>

This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.

This will be useful to minimize the amount of preemption disabling for the -rt patch. It will help leveraging improvements brought by the local_t types in asm/local.h (see Documentation/local_ops.txt). Note that the updates done to variables protected by migrate_disable must be either atomic or protected from concurrent updates done by other threads.

Typical use:

migrate_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migrate_enable();

Which will increment the variable atomically wrt the local CPU.

Changes:

Do a check_migrate() upon migrate_enable() to answer to the migration thread waiting for us to exit the migration disabled critical section. Use a NEED_MIGRATE thread flag for this.

Note: (or we could say FIXME)
Is we ever want to check migration pending in assembly code, we will have to make sure we test the right thread flag bits on each architectures. Care should also be taken to check that the thread flags used won't trigger false positives in non selective asm thread flag checks.

Signed-off-by Mathieu Desnoyers <[email protected]>

Signed-off-by Peter Zijlstra <[email protected]>

---
 include/asm-alpha/thread_info.h     |    3 +
 include/asm-arm/thread_info.h       |    5 +
 include/asm-arm26/thread_info.h     |    5 +
 include/asm-avr32/thread_info.h     |    4 +
 include/asm-blackfin/thread_info.h  |    4 +
 include/asm-cris/thread_info.h      |    4 +
 include/asm-frv/thread_info.h       |    4 +
 include/asm-h8300/thread_info.h     |    4 +
 include/asm-i386/thread_info.h      |    6 +-
 include/asm-ia64/thread_info.h      |    4 +
 include/asm-m32r/thread_info.h      |    4 +
 include/asm-m68k/thread_info.h      |    2 
 include/asm-m68knommu/thread_info.h |    3 +
 include/asm-mips/thread_info.h      |    4 +
 include/asm-parisc/thread_info.h    |    4 +
 include/asm-powerpc/thread_info.h   |    4 +
 include/asm-s390/thread_info.h      |    4 +
 include/asm-sh/thread_info.h        |    4 +
 include/asm-sh64/thread_info.h      |    4 +
 include/asm-sparc/thread_info.h     |    4 +
 include/asm-sparc64/thread_info.h   |    5 +
 include/asm-um/thread_info.h        |    4 +
 include/asm-v850/thread_info.h      |    4 +
 include/asm-x86_64/thread_info.h    |    4 +
 include/asm-xtensa/thread_info.h    |    4 +
 include/linux/preempt.h             |   44 +++++++++++++++++
 kernel/sched.c                      |   91 +++++++++++++++++++++++++++++++++---
 lib/smp_processor_id.c              |    6 +-
 28 files changed, 230 insertions(+), 12 deletions(-)

Index: linux-2.6/include/asm-i386/thread_info.h
===================================================================

include/asm-i386/thread_info.h +4 -2

@@ -31,8 +31,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
-
-
+	int			migrate_count;/* 0: can migrate, <0: BUG */
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead
 						   0-0xFFFFFFFF for kernel-thread

@@ -74,6 +73,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -134,6 +134,7 @@ static inline struct thread_info *curren
 #define TIF_SECCOMP		8	/* secure computing */
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal() */
 #define TIF_NEED_RESCHED_DELAYED 10	/* reschedule on return to userspace */
+#define TIF_NEED_MIGRATE	11	/* migration necessary */
 #define TIF_MEMDIE		16
 #define TIF_DEBUG		17	/* uses debug registers */
 #define TIF_IO_BITMAP		18	/* uses I/O bitmap */

@@ -151,6 +152,7 @@ static inline struct thread_info *curren
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_DEBUG		(1<<TIF_DEBUG)
 #define _TIF_IO_BITMAP		(1<<TIF_IO_BITMAP)
 #define _TIF_FREEZE		(1<<TIF_FREEZE)

Index: linux-2.6/include/linux/preempt.h
===================================================================

include/linux/preempt.h +43 -1

@@ -15,6 +15,8 @@
   extern void notrace sub_preempt_count(unsigned int val);
   extern void notrace mask_preempt_count(unsigned int mask);
   extern void notrace unmask_preempt_count(unsigned int mask);
+  extern void fastcall add_migrate_count(int val);
+  extern void fastcall sub_migrate_count(int val);
 #else
 # define add_preempt_count(val)	do { preempt_count() += (val); } while (0)
 # define sub_preempt_count(val)	do { preempt_count() -= (val); } while (0)

@@ -22,6 +24,8 @@
 		do { preempt_count() |= (mask); } while (0)
 # define unmask_preempt_count(mask) \
 		do { preempt_count() &= ~(mask); } while (0)
+# define add_migrate_count(val) do { migrate_count() += (val); } while (0)
+# define sub_migrate_count(val) do { migrate_count() -= (val); } while (0)
 #endif
 
 #ifdef CONFIG_CRITICAL_TIMING

@@ -35,7 +39,12 @@
 #define inc_preempt_count() add_preempt_count(1)
 #define dec_preempt_count() sub_preempt_count(1)
 
-#define preempt_count()		(current_thread_info()->preempt_count)
+#define preempt_count() (current_thread_info()->preempt_count)
+
+#define inc_migrate_count() add_migrate_count(1)
+#define dec_migrate_count() sub_migrate_count(1)
+
+#define migrate_count() (current_thread_info()->migrate_count)
 
 #ifdef CONFIG_PREEMPT
 

@@ -80,6 +89,36 @@ do { \
 	preempt_check_resched(); \
 } while (0)
 
+#define migrate_disable() \
+do { \
+	inc_migrate_count(); \
+	barrier(); \
+} while (0)
+
+#define migrate_enable_no_check() \
+do { \
+	barrier(); \
+	dec_migrate_count(); \
+} while (0)
+
+#ifdef CONFIG_SMP
+extern void do_check_migrate(void);
+#define check_migrate() \
+do { \
+	if (unlikely(test_thread_flag(TIF_NEED_MIGRATE))) \
+		do_check_migrate(); \
+} while (0)
+#else
+#define check_migrate()
+#endif
+
+#define migrate_enable() \
+do { \
+	migrate_enable_no_check(); \
+	barrier(); \
+	check_migrate(); \
+} while (0)
+
 #else
 
 #define preempt_disable()		do { } while (0)

@@ -91,6 +130,9 @@ do { \
 
 #define preempt_schedule_irq()		do { } while (0)
 
+#define migrate_disable()		do { } while (0)
+#define migrate_enable()		do { } while (0)
+
 #endif
 
 #endif /* __LINUX_PREEMPT_H */

Index: linux-2.6/kernel/sched.c
===================================================================

kernel/sched.c +84 -7

@@ -1175,7 +1175,8 @@ migrate_task(struct task_struct *p, int 
 	 * If the task is not on a runqueue (and not running), then
 	 * it is sufficient to simply update the task's cpu field.
 	 */
-	if (!p->se.on_rq && !task_running(rq, p)) {
+	if (!p->se.on_rq && !task_running(rq, p)
+			&& !task_thread_info(p)->migrate_count) {
 		set_task_cpu(p, dest_cpu);
 		return 0;
 	}

@@ -1506,6 +1507,29 @@ static void balance_rt_tasks(struct rq *
 
 #endif
 
+void fastcall add_migrate_count(int val)
+{
+	/*
+	 * Underflow?
+	 */
+	if (DEBUG_LOCKS_WARN_ON((migrate_count() < 0)))
+		return;
+	migrate_count() += val;
+}
+EXPORT_SYMBOL(add_migrate_count);
+
+void fastcall sub_migrate_count(int val)
+{
+	/*
+	 * Underflow?
+	 */
+	if (DEBUG_LOCKS_WARN_ON(val > migrate_count()))
+		return;
+
+	migrate_count() -= val;
+}
+EXPORT_SYMBOL(sub_migrate_count);
+
 /*
  * find_idlest_cpu - find the idlest cpu among the cpus in group.
  */

@@ -1696,7 +1720,10 @@ try_to_wake_up(struct task_struct *p, un
 #ifdef CONFIG_SMP
 	if (unlikely(task_running(rq, p)))
 		goto out_activate;
-
+#ifdef CONFIG_PREEMPT
+	if (task_thread_info(p)->migrate_count)
+		goto out_activate;
+#endif
 	new_cpu = cpu;
 
 	schedstat_inc(rq, ttwu_cnt);

@@ -1970,6 +1997,7 @@ void sched_fork(struct task_struct *p, i
 #ifdef CONFIG_PREEMPT
 	/* Want to start with kernel preemption disabled. */
 	task_thread_info(p)->preempt_count = 1;
+	task_thread_info(p)->migrate_count = 0;
 #endif
 	put_cpu();
 }

@@ -2435,6 +2463,10 @@ static void sched_migrate_task(struct ta
 	if (!cpu_isset(dest_cpu, p->cpus_allowed)
 	    || unlikely(cpu_is_offline(dest_cpu)))
 		goto out;
+#ifdef CONFIG_PREEMPT
+	if (task_thread_info(p)->migrate_count)
+		goto out;
+#endif
 
 	/* force the process onto the specified CPU */
 	if (migrate_task(p, dest_cpu, &req)) {

@@ -2496,6 +2528,7 @@ int can_migrate_task(struct task_struct 
 	 * 1) running (obviously), or
 	 * 2) cannot be migrated to this CPU due to cpus_allowed, or
 	 * 3) are cache-hot on their current CPU.
+	 * 4) migration preemption is non 0 for this non running task.
 	 */
 	if (!cpu_isset(this_cpu, p->cpus_allowed))
 		return 0;

@@ -2503,6 +2536,10 @@ int can_migrate_task(struct task_struct 
 
 	if (task_running(rq, p))
 		return 0;
+#ifdef CONFIG_PREEMPT
+	if (task_thread_info(p)->migrate_count)
+		return 0;
+#endif
 
 	/*
 	 * Aggressive migration if too many balance attempts have failed:

@@ -3822,6 +3859,27 @@ EXPORT_SYMBOL(schedule);
 
 #ifdef CONFIG_PREEMPT
 
+#ifdef CONFIG_SMP
+/*
+ * Wake up the migration thread to deal with our pending migration.
+ * If we have been moved since, we will just wake up the migration thread from
+ * the wrong CPU, which does not hurt anyone. (that's why we use
+ * raw_smp_processor_id()).
+ */
+void __sched do_check_migrate(void)
+{
+	struct rq *rq;
+
+	if (migrate_count())
+		return;
+
+	clear_thread_flag(TIF_NEED_MIGRATE);
+	rq = cpu_rq(raw_smp_processor_id());
+	wake_up_process(rq->migration_thread);
+}
+EXPORT_SYMBOL(do_check_migrate);
+#endif
+
 /*
  * Global flag to turn preemption off on a CONFIG_PREEMPT kernel:
  */

@@ -5478,7 +5536,7 @@ EXPORT_SYMBOL_GPL(set_cpus_allowed);
  * So we race with normal scheduler movements, but that's OK, as long
  * as the task is no longer on this CPU.
  *
- * Returns non-zero if task was successfully migrated.
+ * Returns non-zero if task is on dest_cpu when this function ends.
  */
 static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
 {

@@ -5500,13 +5558,19 @@ static int __migrate_task(struct task_st
 
 	double_rq_lock(rq_src, rq_dest);
 	/* Already moved. */
-	if (task_cpu(p) != src_cpu)
+	if (task_cpu(p) != src_cpu) {
+		ret = 1;
 		goto out;
+	}
 	/* Affinity changed (again). */
 	if (!cpu_isset(dest_cpu, p->cpus_allowed))
 		goto out;
 
 	on_rq = p->se.on_rq;
+#ifdef CONFIG_PREEMPT
+	if (!on_rq && task_thread_info(p)->migrate_count)
+		goto out;
+#endif
 	if (on_rq)
 		deactivate_task(rq_src, p, 0);
 

@@ -5532,6 +5596,7 @@ static int migration_thread(void *data)
 {
 	int cpu = (long)data;
 	struct rq *rq;
+	int migrated;
 
 	rq = cpu_rq(cpu);
 	BUG_ON(rq->migration_thread != current);

@@ -5567,10 +5632,22 @@ static int migration_thread(void *data)
 		list_del_init(head->next);
 
 		spin_unlock(&rq->lock);
-		__migrate_task(req->task, cpu, req->dest_cpu);
+		migrated = __migrate_task(req->task, cpu, req->dest_cpu);
 		local_irq_enable();
-
-		complete(&req->done);
+		if (!migrated) {
+			/*
+			 * If the process has not been migrated, let it run
+			 * until it reaches a migration_check() so it can
+			 * wake us up.
+			 */
+			spin_lock_irq(&rq->lock);
+			head = &rq->migration_queue;
+			list_add(&req->list, head);
+			set_tsk_thread_flag(req->task, TIF_NEED_MIGRATE);
+			spin_unlock_irq(&rq->lock);
+			wake_up_process(req->task);
+		} else
+			complete(&req->done);
 	}
 	__set_current_state(TASK_RUNNING);
 	return 0;

Index: linux-2.6/include/asm-alpha/thread_info.h
===================================================================

include/asm-alpha/thread_info.h +3 -0

@@ -21,6 +21,7 @@ struct thread_info {
 	mm_segment_t		addr_limit;	/* thread address space */
 	unsigned		cpu;		/* current CPU */
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	int bpt_nsaved;
 	unsigned long bpt_addr[2];		/* breakpoint handling  */

@@ -77,6 +78,7 @@ register struct thread_info *__current_t
 #define TIF_UAC_SIGBUS		8
 #define TIF_MEMDIE		9
 #define TIF_RESTORE_SIGMASK	10	/* restore signal mask in do_signal */
+#define TIF_NEED_MIGRATE	11	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)

@@ -84,6 +86,7 @@ register struct thread_info *__current_t
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 /* Work to do on interrupt/exception return.  */
 #define _TIF_WORK_MASK		(_TIF_NOTIFY_RESUME	\

Index: linux-2.6/include/asm-arm/thread_info.h
===================================================================

include/asm-arm/thread_info.h +5 -0

@@ -51,6 +51,7 @@ struct cpu_context_save {
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain	*exec_domain;	/* execution domain */

@@ -72,6 +73,7 @@ struct thread_info {
 	.exec_domain	= &default_exec_domain,				\
 	.flags		= 0,						\
 	.preempt_count	= 1,						\
+	.migrate_count = 0,						\
 	.addr_limit	= KERNEL_DS,					\
 	.cpu_domain	= domain_val(DOMAIN_USER, DOMAIN_MANAGER) |	\
 			  domain_val(DOMAIN_KERNEL, DOMAIN_MANAGER) |	\

@@ -138,6 +140,7 @@ extern void iwmmxt_task_switch(struct th
  *  TIF_NOTIFY_RESUME	- resumption notification requested
  *  TIF_SIGPENDING	- signal pending
  *  TIF_NEED_RESCHED	- rescheduling necessary
+ *  TIF_NEED_MIGRATE	- migration necessary
  *  TIF_USEDFPU		- FPU was used by this task this quantum (SMP)
  *  TIF_POLLING_NRFLAG	- true if poll_idle() is polling TIF_NEED_RESCHED
  */

@@ -145,6 +148,7 @@ extern void iwmmxt_task_switch(struct th
 #define TIF_SIGPENDING		1
 #define TIF_NEED_RESCHED	2
 #define TIF_NEED_RESCHED_DELAYED 3
+#define TIF_NEED_MIGRATE	4
 #define TIF_SYSCALL_TRACE	8
 #define TIF_POLLING_NRFLAG	16
 #define TIF_USING_IWMMXT	17

@@ -155,6 +159,7 @@ extern void iwmmxt_task_switch(struct th
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_NEED_RESCHED_DELAYED (1<<TIF_NEED_RESCHED_DELAYED)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_USING_IWMMXT	(1 << TIF_USING_IWMMXT)

Index: linux-2.6/include/asm-arm26/thread_info.h
===================================================================

include/asm-arm26/thread_info.h +5 -0

@@ -45,6 +45,7 @@ struct cpu_context_save {
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain      *exec_domain;   /* execution domain */

@@ -60,6 +61,7 @@ struct thread_info {
 	.exec_domain	&default_exec_domain,	\
 	.flags		0,			\
 	.preempt_count	0,			\
+	.migrate_count 0,			\
 	.addr_limit	KERNEL_DS,		\
 	.restart_block  = {                             \
 		.fn     = do_no_restart_syscall,        \

@@ -113,12 +115,14 @@ extern void free_thread_info(struct thre
  *  TIF_NOTIFY_RESUME	- resumption notification requested
  *  TIF_SIGPENDING	- signal pending
  *  TIF_NEED_RESCHED	- rescheduling necessary
+ *  TIF_NEED_MIGRATE	- migration necessary
  *  TIF_USEDFPU		- FPU was used by this task this quantum (SMP)
  *  TIF_POLLING_NRFLAG	- true if poll_idle() is polling TIF_NEED_RESCHED
  */
 #define TIF_NOTIFY_RESUME	0
 #define TIF_SIGPENDING		1
 #define TIF_NEED_RESCHED	2
+#define TIF_NEED_MIGRATE	3
 #define TIF_SYSCALL_TRACE	8
 #define TIF_USED_FPU		16
 #define TIF_POLLING_NRFLAG	17

@@ -127,6 +131,7 @@ extern void free_thread_info(struct thre
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_USED_FPU		(1 << TIF_USED_FPU)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

Index: linux-2.6/include/asm-avr32/thread_info.h
===================================================================

include/asm-avr32/thread_info.h +4 -0

@@ -25,6 +25,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;
 	__s32			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 	__u8			supervisor_stack[0];
 };

@@ -36,6 +37,7 @@ struct thread_info {
 	.flags		= 0,						\
 	.cpu		= 0,						\
 	.preempt_count	= 1,						\
+	.migrate_count = 0,						\
 	.restart_block	= {						\
 		.fn	= do_no_restart_syscall				\
 	}								\

@@ -84,6 +86,7 @@ static inline struct thread_info *curren
 #define TIF_MEMDIE		7
 #define TIF_RESTORE_SIGMASK	8	/* restore signal mask in do_signal */
 #define TIF_CPU_GOING_TO_SLEEP	9	/* CPU is entering sleep 0 mode */
+#define TIF_NEED_MIGRATE      10       /* migration necessary */
 #define TIF_USERSPACE		31      /* true if FS sets userspace */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)

@@ -96,6 +99,7 @@ static inline struct thread_info *curren
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_CPU_GOING_TO_SLEEP (1 << TIF_CPU_GOING_TO_SLEEP)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 /* XXX: These two masks must never span more than 16 bits! */
 /* work to do on interrupt/exception return */

Index: linux-2.6/include/asm-blackfin/thread_info.h
===================================================================

include/asm-blackfin/thread_info.h +4 -0

@@ -54,6 +54,7 @@ struct thread_info {
 	unsigned long flags;	/* low level flags */
 	int cpu;		/* cpu we're on */
 	int preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int migrate_count;	/* 0: can migrate, <0 => BUG */
 	mm_segment_t addr_limit;	/* address limit */
 	struct restart_block restart_block;
 	struct l1_scratch_task_info l1_task_info;

@@ -69,6 +70,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count  = 1,                    \
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -126,6 +128,7 @@ static inline struct thread_info *curren
 #define TIF_MEMDIE              5
 #define TIF_RESTORE_SIGMASK	6	/* restore signal mask in do_signal() */
 #define TIF_FREEZE              7       /* is freezing for suspend */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -135,6 +138,7 @@ static inline struct thread_info *curren
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_FREEZE             (1<<TIF_FREEZE)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 

Index: linux-2.6/include/asm-cris/thread_info.h
===================================================================

include/asm-cris/thread_info.h +4 -0

@@ -32,6 +32,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead

@@ -58,6 +59,7 @@ struct thread_info {
 	.flags		= 0,				\
 	.cpu		= 0,				\
 	.preempt_count	= 1,				\
+	.migrate_count = 0,				\
 	.addr_limit	= KERNEL_DS,			\
 	.restart_block = {				\
 		       .fn = do_no_restart_syscall,	\

@@ -82,6 +84,7 @@ struct thread_info {
 #define TIF_NOTIFY_RESUME	1	/* resumption notification requested */
 #define TIF_SIGPENDING		2	/* signal pending */
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
+#define TIF_NEED_MIGRATE	4	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17
 

@@ -90,6 +93,7 @@ struct thread_info {
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

Index: linux-2.6/include/asm-frv/thread_info.h
===================================================================

include/asm-frv/thread_info.h +4 -0

@@ -36,6 +36,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thead

@@ -68,6 +69,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -114,6 +116,7 @@ register struct thread_info *__current_t
 #define TIF_SINGLESTEP		4	/* restore singlestep on return to user mode */
 #define TIF_IRET		5	/* return with iret */
 #define TIF_RESTORE_SIGMASK	6	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17	/* OOM killer killed process */
 #define TIF_FREEZE		18	/* freezing for suspend */

@@ -127,6 +130,7 @@ register struct thread_info *__current_t
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_FREEZE		(1 << TIF_FREEZE)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

Index: linux-2.6/include/asm-h8300/thread_info.h
===================================================================

include/asm-h8300/thread_info.h +4 -0

@@ -24,6 +24,7 @@ struct thread_info {
 	unsigned long	   flags;		/* low level flags */
 	int		   cpu;			/* cpu we're on */
 	int		   preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };
 

@@ -37,6 +38,7 @@ struct thread_info {
 	.flags =	0,			\
 	.cpu =		0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -92,6 +94,7 @@ static inline struct thread_info *curren
 #define TIF_POLLING_NRFLAG	4	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		5
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -99,6 +102,7 @@ static inline struct thread_info *curren
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 

Index: linux-2.6/include/asm-ia64/thread_info.h
===================================================================

include/asm-ia64/thread_info.h +4 -0

@@ -30,6 +30,7 @@ struct thread_info {
 	__u32 status;			/* Thread synchronous flags */
 	mm_segment_t addr_limit;	/* user-level address space limit */
 	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
+	int migrate_count;		/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };
 

@@ -43,6 +44,7 @@ struct thread_info {
 	.cpu		= 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.preempt_count	= 0,			\
+	.migrate_count = 0,			\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -86,6 +88,7 @@ struct thread_info {
 #define TIF_SYSCALL_AUDIT	4	/* syscall auditing active */
 #define TIF_SINGLESTEP		5	/* restore singlestep on return to user mode */
 #define TIF_RESTORE_SIGMASK	6	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		17
 #define TIF_MCA_INIT		18	/* this task is processing MCA or INIT */

@@ -99,6 +102,7 @@ struct thread_info {
 #define _TIF_SYSCALL_TRACEAUDIT	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SINGLESTEP)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)

Index: linux-2.6/include/asm-m32r/thread_info.h
===================================================================

include/asm-m32r/thread_info.h +4 -0

@@ -29,6 +29,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thread

@@ -69,6 +70,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -151,6 +153,7 @@ static inline unsigned int get_thread_fa
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_SINGLESTEP		4	/* restore singlestep on return to user mode */
 #define TIF_IRET		5	/* return with iret */
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 					/* 31..28 fault code */
 #define TIF_MEMDIE		17

@@ -162,6 +165,7 @@ static inline unsigned int get_thread_fa
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_IRET		(1<<TIF_IRET)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x0000FFFF	/* work to do on any return to u-space */

Index: linux-2.6/include/asm-m68k/thread_info.h
===================================================================

include/asm-m68k/thread_info.h +2 -0

@@ -9,6 +9,7 @@ struct thread_info {
 	unsigned long		flags;
 	struct exec_domain	*exec_domain;	/* execution domain */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u32 cpu; /* should always be 0 on m68k */
 	struct restart_block    restart_block;
 };

@@ -58,5 +59,6 @@ struct thread_info {
 #define TIF_DELAYED_TRACE	14	/* single step a syscall */
 #define TIF_SYSCALL_TRACE	15	/* syscall trace active */
 #define TIF_MEMDIE		16
+#define TIF_NEED_MIGRATE	17	/* migration necessary */
 
 #endif	/* _ASM_M68K_THREAD_INFO_H */

Index: linux-2.6/include/asm-m68knommu/thread_info.h
===================================================================

include/asm-m68knommu/thread_info.h +3 -0

@@ -37,6 +37,7 @@ struct thread_info {
 	unsigned long	   flags;		/* low level flags */
 	int		   cpu;			/* cpu we're on */
 	int		   preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int		   migrate_count;	/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };
 

@@ -89,6 +90,7 @@ static inline struct thread_info *curren
 #define TIF_POLLING_NRFLAG	4	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		5
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -96,6 +98,7 @@ static inline struct thread_info *curren
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 #define _TIF_WORK_MASK		0x0000FFFE	/* work to do on interrupt/exception return */
 

Index: linux-2.6/include/asm-mips/thread_info.h
===================================================================

include/asm-mips/thread_info.h +4 -0

@@ -28,6 +28,7 @@ struct thread_info {
 	unsigned long		tp_value;	/* thread pointer */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 						   0-0xBFFFFFFF for user-thead

@@ -49,6 +50,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -115,6 +117,7 @@ register struct thread_info *__current_t
 #define TIF_SYSCALL_AUDIT	4	/* syscall auditing active */
 #define TIF_SECCOMP		5	/* secure computing */
 #define TIF_NEED_RESCHED_DELAYED 6	/* reschedule on return to userspace */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal() */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */

@@ -129,6 +132,7 @@ register struct thread_info *__current_t
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_NEED_RESCHED_DELAYED (1<<TIF_NEED_RESCHED_DELAYED)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)

Index: linux-2.6/include/asm-parisc/thread_info.h
===================================================================

include/asm-parisc/thread_info.h +4 -0

@@ -13,6 +13,7 @@ struct thread_info {
 	mm_segment_t addr_limit;	/* user-level address space limit */
 	__u32 cpu;			/* current CPU */
 	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
+	int migrate_count;		/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 };
 

@@ -24,6 +25,7 @@ struct thread_info {
 	.cpu		= 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
   	.restart_block	= {			\
 		.fn = do_no_restart_syscall	\
 	}					\

@@ -63,6 +65,7 @@ struct thread_info {
 #define TIF_32BIT               5       /* 32 bit binary */
 #define TIF_MEMDIE		6
 #define TIF_RESTORE_SIGMASK	7	/* restore saved signal mask */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)

@@ -71,6 +74,7 @@ struct thread_info {
 #define _TIF_POLLING_NRFLAG	(1 << TIF_POLLING_NRFLAG)
 #define _TIF_32BIT		(1 << TIF_32BIT)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #define _TIF_USER_WORK_MASK     (_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | \
                                  _TIF_NEED_RESCHED | _TIF_RESTORE_SIGMASK)

Index: linux-2.6/include/asm-powerpc/thread_info.h
===================================================================

include/asm-powerpc/thread_info.h +4 -0

@@ -35,6 +35,7 @@ struct thread_info {
 	int		cpu;			/* cpu we're on */
 	int		preempt_count;		/* 0 => preemptable,
 						   <0 => BUG */
+	int		migrate_count;	/* 0: can migrate, <0 => BUG */
 	struct restart_block restart_block;
 	unsigned long	local_flags;		/* private flags for thread */
 

@@ -53,6 +54,7 @@ struct thread_info {
 	.exec_domain =	&default_exec_domain,	\
 	.cpu =		0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -124,6 +126,7 @@ static inline struct thread_info *curren
 #define TIF_NOERROR		14	/* Force successful syscall return */
 #define TIF_RESTORE_SIGMASK	15	/* Restore signal mask in do_signal */
 #define TIF_FREEZE		16	/* Freezing for suspend */
+#define TIF_NEED_MIGRATE	17	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -143,6 +146,7 @@ static inline struct thread_info *curren
 #define _TIF_FREEZE		(1<<TIF_FREEZE)
 #define _TIF_NEED_RESCHED_DELAYED (1<<TIF_NEED_RESCHED_DELAYED)
 
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SYSCALL_T_OR_A	(_TIF_SYSCALL_TRACE|_TIF_SYSCALL_AUDIT|_TIF_SECCOMP)
 
 #define _TIF_USER_WORK_MASK	(_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | \

Index: linux-2.6/include/asm-s390/thread_info.h
===================================================================

include/asm-s390/thread_info.h +4 -0

@@ -51,6 +51,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	unsigned int		cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 };
 

@@ -64,6 +65,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\

@@ -96,6 +98,7 @@ static inline struct thread_info *curren
 #define TIF_SYSCALL_AUDIT	5	/* syscall auditing active */
 #define TIF_SINGLE_STEP		6	/* deliver sigtrap on return to user */
 #define TIF_MCCK_PENDING	7	/* machine check handling is pending */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling 
 					   TIF_NEED_RESCHED */

@@ -110,6 +113,7 @@ static inline struct thread_info *curren
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_SINGLE_STEP	(1<<TIF_SINGLE_STEP)
 #define _TIF_MCCK_PENDING	(1<<TIF_MCCK_PENDING)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_31BIT		(1<<TIF_31BIT)

Index: linux-2.6/include/asm-sh/thread_info.h
===================================================================

include/asm-sh/thread_info.h +4 -0

@@ -21,6 +21,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block	restart_block;
 	unsigned long		previous_sp;	/* sp of previous stack in case

@@ -58,6 +59,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -113,6 +115,7 @@ static inline struct thread_info *curren
 #define TIF_RESTORE_SIGMASK	4	/* restore signal mask in do_signal() */
 #define TIF_SINGLESTEP		5	/* singlestepping active */
 #define TIF_NEED_RESCHED_DELAYED	6	/* reschedule on return to userspace */
+#define TIF_NEED_MIGRATE	7	/* migration necessary */
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		18

@@ -125,6 +128,7 @@ static inline struct thread_info *curren
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_NEED_RESCHED_DELAYED	(1<<TIF_NEED_RESCHED_DELAYED)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_FREEZE		(1<<TIF_FREEZE)

Index: linux-2.6/include/asm-sh64/thread_info.h
===================================================================

include/asm-sh64/thread_info.h +4 -0

@@ -23,6 +23,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	/* Put the 4 32-bit fields together to make asm offsetting easier. */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u16			cpu;
 
 	mm_segment_t		addr_limit;

@@ -41,6 +42,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit     = KERNEL_DS,            \
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\

@@ -79,12 +81,14 @@ static inline struct thread_info *curren
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_MEMDIE		4
 #define TIF_RESTORE_SIGMASK	5	/* Restore signal mask in do_signal */
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #endif /* __KERNEL__ */
 

Index: linux-2.6/include/asm-sparc/thread_info.h
===================================================================

include/asm-sparc/thread_info.h +4 -0

@@ -33,6 +33,7 @@ struct thread_info {
 	int			cpu;		/* cpu we're on */
 	int			preempt_count;	/* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	int			softirq_count;
 	int			hardirq_count;
 

@@ -65,6 +66,7 @@ struct thread_info {
 	.flags		=	0,			\
 	.cpu		=	0,			\
 	.preempt_count	=	1,			\
+	.migrate_count =	0,			\
 	.restart_block	= {				\
 		.fn	=	do_no_restart_syscall,	\
 	},						\

@@ -132,6 +134,7 @@ BTFIXUPDEF_CALL(void, free_thread_info, 
 #define TIF_SIGPENDING		2	/* signal pending */
 #define TIF_NEED_RESCHED	3	/* rescheduling necessary */
 #define TIF_RESTORE_SIGMASK	4	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	5	/* migration necessary */
 #define TIF_USEDFPU		8	/* FPU was used by this task
 					 * this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	9	/* true if poll_idle() is polling

@@ -143,6 +146,7 @@ BTFIXUPDEF_CALL(void, free_thread_info, 
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 

Index: linux-2.6/include/asm-sparc64/thread_info.h
===================================================================

include/asm-sparc64/thread_info.h +4 -1

@@ -47,6 +47,7 @@ struct thread_info {
 	struct pt_regs		*kregs;
 	struct exec_domain	*exec_domain;
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	__u8			new_child;
 	__u8			syscall_noerror;
 	__u16			cpu;

@@ -137,6 +138,7 @@ struct thread_info {
 	.flags		= ((unsigned long)ASI_P) << TI_FLAG_CURRENT_DS_SHIFT,	\
 	.exec_domain	=	&default_exec_domain,	\
 	.preempt_count	=	1,			\
+	.migrate_count =	0,			\
 	.restart_block	= {				\
 		.fn	=	do_no_restart_syscall,	\
 	},						\

@@ -225,7 +227,7 @@ register struct thread_info *current_thr
 #define TIF_UNALIGNED		5	/* allowed to do unaligned accesses */
 #define TIF_NEWSIGNALS		6	/* wants new-style signals */
 #define TIF_32BIT		7	/* 32-bit binary */
-/* flag bit 8 is available */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 #define TIF_SECCOMP		9	/* secure computing */
 #define TIF_SYSCALL_AUDIT	10	/* syscall auditing active */
 /* flag bit 11 is available */

@@ -244,6 +246,7 @@ register struct thread_info *current_thr
 #define _TIF_UNALIGNED		(1<<TIF_UNALIGNED)
 #define _TIF_NEWSIGNALS		(1<<TIF_NEWSIGNALS)
 #define _TIF_32BIT		(1<<TIF_32BIT)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_SYSCALL_AUDIT	(1<<TIF_SYSCALL_AUDIT)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)

Index: linux-2.6/include/asm-um/thread_info.h
===================================================================

include/asm-um/thread_info.h +4 -0

@@ -18,6 +18,7 @@ struct thread_info {
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;  /* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user
 						   0-0xFFFFFFFF for kernel */

@@ -32,6 +33,7 @@ struct thread_info {
 	.flags =		0,		\
 	.cpu =		0,			\
 	.preempt_count =	1,		\
+	.migrate_count =	0,		\
 	.addr_limit =	KERNEL_DS,		\
 	.restart_block =  {			\
 		.fn =  do_no_restart_syscall,	\

@@ -71,6 +73,7 @@ static inline struct thread_info *curren
 #define TIF_MEMDIE	 	5
 #define TIF_SYSCALL_AUDIT	6
 #define TIF_RESTORE_SIGMASK	7
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SIGPENDING		(1 << TIF_SIGPENDING)

@@ -79,5 +82,6 @@ static inline struct thread_info *curren
 #define _TIF_MEMDIE		(1 << TIF_MEMDIE)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_RESTORE_SIGMASK	(1 << TIF_RESTORE_SIGMASK)
+#define _TIF_NEED_MIGRATE	(1 << TIF_NEED_MIGRATE)
 
 #endif

Index: linux-2.6/include/asm-v850/thread_info.h
===================================================================

include/asm-v850/thread_info.h +4 -0

@@ -32,6 +32,7 @@ struct thread_info {
 	int			cpu;		/* cpu we're on */
 	int			preempt_count;	/* 0 => preemptable,
 						   <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 	struct restart_block	restart_block;
 };
 

@@ -42,6 +43,7 @@ struct thread_info {
 	.flags =	0,						      \
 	.cpu =		0,						      \
 	.preempt_count = 1,						      \
+	.migrate_count = 0,						      \
 	.restart_block = {						      \
 		.fn = do_no_restart_syscall,				      \
 	},								      \

@@ -83,6 +85,7 @@ struct thread_info {
 #define TIF_POLLING_NRFLAG	4	/* true if poll_idle() is polling
 					   TIF_NEED_RESCHED */
 #define TIF_MEMDIE		5
+#define TIF_NEED_MIGRATE	6	/* migration necessary */
 
 /* as above, but as bit values */
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -90,6 +93,7 @@ struct thread_info {
 #define _TIF_SIGPENDING		(1<<TIF_SIGPENDING)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 
 
 /* Size of kernel stack for each process.  */

Index: linux-2.6/include/asm-x86_64/thread_info.h
===================================================================

include/asm-x86_64/thread_info.h +4 -0

@@ -30,6 +30,7 @@ struct thread_info {
 	__u32			status;		/* thread synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int 			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	
 	struct restart_block    restart_block;

@@ -48,6 +49,7 @@ struct thread_info {
 	.flags	       = 0,			\
 	.cpu	       = 0,			\
 	.preempt_count = 1,			\
+	.migrate_count = 0,			\
 	.addr_limit     = KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -116,6 +118,7 @@ static inline struct thread_info *stack_
 #define TIF_SYSCALL_AUDIT	7	/* syscall auditing active */
 #define TIF_SECCOMP		8	/* secure computing */
 #define TIF_RESTORE_SIGMASK	9	/* restore signal mask in do_signal */
+#define TIF_NEED_MIGRATE	11	/* migration necessary */
 /* 16 free */
 #define TIF_IA32		17	/* 32bit process */ 
 #define TIF_FORK		18	/* ret_from_fork */

@@ -135,6 +138,7 @@ static inline struct thread_info *stack_
 #define _TIF_SECCOMP		(1<<TIF_SECCOMP)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 #define _TIF_NEED_RESCHED_DELAYED (1<<TIF_NEED_RESCHED_DELAYED)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_IA32		(1<<TIF_IA32)
 #define _TIF_FORK		(1<<TIF_FORK)
 #define _TIF_ABI_PENDING	(1<<TIF_ABI_PENDING)

Index: linux-2.6/include/asm-xtensa/thread_info.h
===================================================================

include/asm-xtensa/thread_info.h +4 -0

@@ -34,6 +34,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	__s32			preempt_count;	/* 0 => preemptable,< 0 => BUG*/
+	__s32			migrate_count;/* 0: can migrate, <0 => BUG */
 
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block    restart_block;

@@ -72,6 +73,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.migrate_count = 0,			\
 	.addr_limit	= KERNEL_DS,		\
 	.restart_block = {			\
 		.fn = do_no_restart_syscall,	\

@@ -117,6 +119,7 @@ static inline struct thread_info *curren
 #define TIF_IRET		5	/* return with iret */
 #define TIF_MEMDIE		6
 #define TIF_RESTORE_SIGMASK	7	/* restore signal mask in do_signal() */
+#define TIF_NEED_MIGRATE	8	/* migration necessary */
 #define TIF_POLLING_NRFLAG	16	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)

@@ -125,6 +128,7 @@ static inline struct thread_info *curren
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_SINGLESTEP		(1<<TIF_SINGLESTEP)
 #define _TIF_IRET		(1<<TIF_IRET)
+#define _TIF_NEED_MIGRATE	(1<<TIF_NEED_MIGRATE)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
 #define _TIF_RESTORE_SIGMASK	(1<<TIF_RESTORE_SIGMASK)
 

Index: linux-2.6/lib/smp_processor_id.c
===================================================================

lib/smp_processor_id.c +5 -2

@@ -10,12 +10,16 @@
 unsigned int notrace debug_smp_processor_id(void)
 {
 	unsigned long preempt_count = preempt_count();
+	unsigned long migrate_count = migrate_count();
 	int this_cpu = raw_smp_processor_id();
 	cpumask_t this_mask;
 
 	if (likely(preempt_count))
 		goto out;
 
+	if (likely(migrate_count))
+		goto out;
+
 	if (irqs_disabled())
 		goto out;
 

@@ -42,7 +46,7 @@ unsigned int notrace debug_smp_processor
 	if (!printk_ratelimit())
 		goto out_enable;
 
-	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] code: %s/%d\n", preempt_count()-1, current->comm, current->pid);
+	printk(KERN_ERR "BUG: using smp_processor_id() in preemptible [%08x] migration [%08x] code: %s/%d\n", preempt_count()-1, migrate_count(), current->comm, current->pid);
 	print_symbol("caller is %s\n", (long)__builtin_return_address(0));
 	dump_stack();
 
 
--

From: Mathieu Desnoyers <[email protected]>

This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.

This will be useful to minimize the amount of preemption disabling for the -rt patch. It will help leveraging improvements brought by the local_t types in asm/local.h (see Documentation/local_ops.txt). Note that the updates done to variables protected by migrate_disable must be either atomic or protected from concurrent updates done by other threads.

Typical use:

migrate_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migrate_enable();

Which will increment the variable atomically wrt the local CPU.

Quoted 18 lines · Peter Zijlstra

From: Mathieu Desnoyers <[email protected]>

This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.

This will be useful to minimize the amount of preemption disabling for the -rt patch. It will help leveraging improvements brought by the local_t types in asm/local.h (see Documentation/local_ops.txt). Note that the updates done to variables protected by migrate_disable must be either atomic or protected from concurrent updates done by other threads.

Typical use:

migrate_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migrate_enable();

Quoted 1 line

Which will increment the variable atomically wrt the local CPU.

I still think this patch is buggy. Perhaps I am wrong. Please look at

	http://marc.info/?l=linux-kernel&m=118417177818825

there was no any reply.

Quoted 18 lines · Peter Zijlstra

From: Mathieu Desnoyers <[email protected]>

This patch adds the ability to protect critical sections from migration to another CPU without disabling preemption.

This will be useful to minimize the amount of preemption disabling for the -rt patch. It will help leveraging improvements brought by the local_t types in asm/local.h (see Documentation/local_ops.txt). Note that the updates done to variables protected by migrate_disable must be either atomic or protected from concurrent updates done by other threads.

Typical use:

migrate_disable();
local_inc(&__get_cpu_var(&my_local_t_var));
migrate_enable();

Quoted 1 line

Which will increment the variable atomically wrt the local CPU.

I still think this patch is buggy. Perhaps I am wrong. Please look at

	http://marc.info/?l=linux-kernel&m=118417177818825

there was no any reply.

How about somethign like this?

---

Avoid busy looping on unmigratable tasks by pushing the migration requests onto a delayed_migration_queue, which we try on each wakeup.

Signed-off-by Peter Zijlstra <[email protected]>

---
 kernel/sched.c |   10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================

kernel/sched.c +8 -2

@@ -288,6 +288,7 @@ struct rq {
 
 	struct task_struct *migration_thread;
 	struct list_head migration_queue;
+	struct list_head delayed_migration_queue;
 #endif
 
 #ifdef CONFIG_SCHEDSTATS

@@ -5623,6 +5624,11 @@ static int migration_thread(void *data)
 		head = &rq->migration_queue;
 
 		if (list_empty(head)) {
+			/*
+			 * we got a wakeup, give the delayed list another shot.
+			 */
+			if (current->state != TASK_INTERRUPTIBLE)
+				list_splice(&rq->delayed_migration_queue, head);
 			spin_unlock_irq(&rq->lock);
 			schedule();
 			set_current_state(TASK_INTERRUPTIBLE);

@@ -5641,8 +5647,7 @@ static int migration_thread(void *data)
 			 * wake us up.
 			 */
 			spin_lock_irq(&rq->lock);
-			head = &rq->migration_queue;
-			list_add(&req->list, head);
+			list_add(&req->list, &rq->delayed_migration_queue);
 			set_tsk_thread_flag(req->task, TIF_NEED_MIGRATE);
 			spin_unlock_irq(&rq->lock);
 			wake_up_process(req->task);

@@ -7006,6 +7011,7 @@ void __init sched_init(void)
 		rq->cpu = i;
 		rq->migration_thread = NULL;
 		INIT_LIST_HEAD(&rq->migration_queue);
+		INIT_LIST_HEAD(&rq->delayed_migration_queue);
 #endif
 		atomic_set(&rq->nr_iowait, 0);
 

kernel/sched.c struct rq { · line 292

Quoted 8 lines · Peter Zijlstra

kernel/sched.c +1 -0

@@ -288,6 +288,7 @@ struct rq {
 
 	struct task_struct *migration_thread;
 	struct list_head migration_queue;
+	struct list_head delayed_migration_queue;
 #endif

I think this could be simplified a bit.

delayed_migration_queue can be a local variable in migration_thread(), then

Quoted 4 lines

kernel/sched.c +0 -0

 #ifdef CONFIG_SCHEDSTATS

@@ -5623,6 +5624,11 @@ static int migration_thread(void *data)
 		head = &rq->migration_queue;
 

kernel/sched.c static int migration_thread(void *data) · line 5631

Quoted 6 lines

kernel/sched.c +5 -0

 		if (list_empty(head)) {
+			/*
+			 * we got a wakeup, give the delayed list another shot.
+			 */
+			if (current->state != TASK_INTERRUPTIBLE)
+				list_splice(&rq->delayed_migration_queue, head);

No need to check TASK_INTERRUPTIBLE, just do list_splice() unconditionally and call schedule().

===================================================================
---
linux-2.6.22-rc6-mm1.orig/include/asm-generic/local.h 2007-07-12
19:44:18.000000000 -0700
+++ linux-2.6.22-rc6-mm1/include/asm-generic/local.h 2007-07-12
19:44:57.000000000 -0700

From: Christoph Lameter <[email protected]>

Signed-off-by Peter Zijlstra <[email protected]>

---
 include/asm-generic/local.h |   25 +++++++++++++++++++++++--
 include/asm-i386/local.h    |   13 +++++++++++++
 include/asm-x86_64/local.h  |   16 ++++++++++++++++
 3 files changed, 52 insertions(+), 2 deletions(-)

Index: linux-2.6.22-rc6-mm1/include/asm-generic/local.h
===================================================================

include/asm-generic/local.h +0 -2

@@ -46,13 +46,34 @@ typedef struct
 #define local_add_unless(l, a, u) atomic_long_add_unless((&(l)->a), (a), (u))
 #define local_inc_not_zero(l) atomic_long_inc_not_zero(&(l)->a)
 
-/* Non-atomic variants, ie. preemption disabled and won't be touched
- * in interrupt, etc.  Some archs can optimize this case well. */

include/asm-generic/local.h +7 -0

+#define __local_xchg((v), (n)) 						\
+({									\
+	__typeof(v) x = *(v);						\
+	*(v) = (n);							\
+	x;								\
+)}
+
 /* Use these for per-cpu local_t variables: on some archs they are
  * much more efficient than these naive implementations.  Note they take
  * a variable (eg. mystruct.foo), not an address.

Index: linux-2.6.22-rc6-mm1/include/asm-x86_64/local.h
===================================================================

include/asm-x86_64/local.h +1 -0

+
 /* Use these for per-cpu local_t variables: on some archs they are
  * much more efficient than these naive implementations.  Note they take
  * a variable, not an address.

Index: linux-2.6.22-rc6-mm1/include/asm-i386/local.h
===================================================================

include/asm-i386/local.h +0 -0

@@ -194,12 +194,25 @@ static __inline__ long local_sub_return(
 })
 #define local_inc_not_zero(l) local_add_unless((l), 1, 0)

include/asm-i386/local.h +0 -1

 /* Use these for per-cpu local_t variables: on some archs they are
  * much more efficient than these naive implementations.  Note they take
  * a variable, not an address.
 
--

Quoted 19 lines · * Peter Zijlstra ([email protected]) wrote:

From: Christoph Lameter <[email protected]>

Signed-off-by Peter Zijlstra <[email protected]>

---
 include/asm-generic/local.h |   25 +++++++++++++++++++++++--
 include/asm-i386/local.h    |   13 +++++++++++++
 include/asm-x86_64/local.h  |   16 ++++++++++++++++
 3 files changed, 52 insertions(+), 2 deletions(-)

Index: linux-2.6.22-rc6-mm1/include/asm-generic/local.h
===================================================================

include/asm-generic/local.h +0 -2

@@ -46,13 +46,34 @@ typedef struct
 #define local_add_unless(l, a, u) atomic_long_add_unless((&(l)->a), (a), (u))
 #define local_inc_not_zero(l) atomic_long_inc_not_zero(&(l)->a)
 
-/* Non-atomic variants, ie. preemption disabled and won't be touched
- * in interrupt, etc.  Some archs can optimize this case well. */

include/asm-generic/local.h typedef struct · line 58

Quoted 10 lines

include/asm-generic/local.h +10 -0

+/*
+ * Establish a state necessary for __local_xx functions to work.
+ */
+#define __local_begin(flags)	local_irq_disable(flags)
+
+static inline void __local_end(unsigned long flags)
+{
+	local_irq_restore(flags);
+}
+

Wouldn't it be cheaper to use preempt_disable/enable instead of irq disable/enable in asm-generic to protect the __local accesses since they are not supposed to be touched by interrupt context ?

I also think that __local_begin/end() should be changed into local_begin() and local_end(). It makes sense to use this around all local_t variable accesses.

Quoted 10 lines

include/asm-generic/local.h +5 -0

+/*
+ * Non-atomic variants, ie. within local_begin() / local_end() or
+ * preempt_disable / enable() and won't be touched in interrupt, etc.
+ * Some archs can optimize this case well.
+ */
 #define __local_inc(l)		local_set((l), local_read(l) + 1)
 #define __local_dec(l)		local_set((l), local_read(l) - 1)
 #define __local_add(i,l)	local_set((l), local_read(l) + (i))
 #define __local_sub(i,l)	local_set((l), local_read(l) - (i))
 

include/asm-generic/local.h typedef struct · line 69

Quoted 1 line

include/asm-generic/local.h +1 -0

+#define __local_cmpxchg((v), (o), (n)) (*(v) = (n), (o))

Shouldn't this look like a while loop instead ? Where is the comparison ? It should use local_set and local_read...

The proper way to do this would be to take all architectures that only define a atomic_cmpxchg and atomic_xchg and turn that into a cmpxchg and xchg. Then, the same could be done for architectures which only have a local_cmpxchg, but no cmpxchg_local.

Then, cmpxchg_local could be used to touch a variable in an atomic wrt cpu fashion without wrapping the variable in a local_t.

All the local_*() functions should only touch local_t types.

If local_begin()/local_end() is defined as preempt disable/enable, then it's ok to use this to protect __local_*() accesses. However, if you turn this into a migrate_disable/enable(), then the protection against other threads on the same CPU is not insured.

Quoted 49 lines · Mathieu Desnoyers

Quoted 19 lines · * Peter Zijlstra ([email protected]) wrote:

From: Christoph Lameter <[email protected]>

Signed-off-by Peter Zijlstra <[email protected]>

---
 include/asm-generic/local.h |   25 +++++++++++++++++++++++--
 include/asm-i386/local.h    |   13 +++++++++++++
 include/asm-x86_64/local.h  |   16 ++++++++++++++++
 3 files changed, 52 insertions(+), 2 deletions(-)

Index: linux-2.6.22-rc6-mm1/include/asm-generic/local.h
===================================================================

include/asm-generic/local.h +0 -2

@@ -46,13 +46,34 @@ typedef struct
 #define local_add_unless(l, a, u) atomic_long_add_unless((&(l)->a), (a), (u))
 #define local_inc_not_zero(l) atomic_long_inc_not_zero(&(l)->a)
 
-/* Non-atomic variants, ie. preemption disabled and won't be touched
- * in interrupt, etc.  Some archs can optimize this case well. */

include/asm-generic/local.h typedef struct · line 58

Quoted 10 lines

include/asm-generic/local.h +10 -0

+/*
+ * Establish a state necessary for __local_xx functions to work.
+ */
+#define __local_begin(flags)	local_irq_disable(flags)
+
+static inline void __local_end(unsigned long flags)
+{
+	local_irq_restore(flags);
+}
+

Wouldn't it be cheaper to use preempt_disable/enable instead of irq disable/enable in asm-generic to protect the __local accesses since they are not supposed to be touched by interrupt context ?

I also think that __local_begin/end() should be changed into local_begin() and local_end(). It makes sense to use this around all local_t variable accesses.

Quoted 10 lines

include/asm-generic/local.h +5 -0

+/*
+ * Non-atomic variants, ie. within local_begin() / local_end() or
+ * preempt_disable / enable() and won't be touched in interrupt, etc.
+ * Some archs can optimize this case well.
+ */
 #define __local_inc(l)		local_set((l), local_read(l) + 1)
 #define __local_dec(l)		local_set((l), local_read(l) - 1)
 #define __local_add(i,l)	local_set((l), local_read(l) + (i))
 #define __local_sub(i,l)	local_set((l), local_read(l) - (i))
 

Quoted 4 lines

include/asm-generic/local.h typedef struct · line 69

Quoted 1 line

include/asm-generic/local.h +1 -0

+#define __local_cmpxchg((v), (o), (n)) (*(v) = (n), (o))

Shouldn't this look like a while loop instead ? Where is the comparison ? It should use local_set and local_read...

Yeah, needs more thought.

Quoted 8 lines

The proper way to do this would be to take all architectures that only define a atomic_cmpxchg and atomic_xchg and turn that into a cmpxchg and xchg. Then, the same could be done for architectures which only have a local_cmpxchg, but no cmpxchg_local.

Then, cmpxchg_local could be used to touch a variable in an atomic wrt cpu fashion without wrapping the variable in a local_t.

Quoted 6 lines

All the local_*() functions should only touch local_t types.

If local_begin()/local_end() is defined as preempt disable/enable, then it's ok to use this to protect __local_*() accesses. However, if you turn this into a migrate_disable/enable(), then the protection against other threads on the same CPU is not insured.

Yeah, the generic stuff is rather broken. For -rt begin/end should map to migrate_disable/enable, and the primitives could be done using preempt_disable/enable.

something like so:

static inline void local_begin(flags)

{
	migrate_disable();
}

static inline void local_end(flags)

{
	migrate_enable();
}

#define __local_cmpxchg(__p, __o, __n) \

({	typeof(__o) o;				\
	preempt_disable();			\
	o = *(__p);				\
	if (o == (__o))				\
		*(__p) = __n;			\
	preempt_enable();			\
	o; })

Obviously that only works for -rt.

Signed-off-by Peter Zijlstra <[email protected]>

---
 include/asm-i386/local.h   |    7 ++++---
 include/asm-x86_64/local.h |    7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

Index: linux-2.6/include/asm-i386/local.h
===================================================================

include/asm-i386/local.h +3 -2

 }
 
-static inline void __local_end(unsigned long flags) {
-	preempt_enable();
+static inline void __local_end(unsigned long flags)
+{
+	migrate_enable();
 }
 
 /* On x86, these are no better than the atomic variants. */

Index: linux-2.6/include/asm-x86_64/local.h
===================================================================

include/asm-x86_64/local.h +4 -4

@@ -186,11 +186,12 @@ static __inline__ long local_sub_return(
 #define __local_begin(__flags)		\
 {					\
 	(__flags) = 0;			\
-	preempt_disable();		\
+	migrate_disable();		\
 }
 
-static inline void __local_end(unsigned long flags) {
-	preempt_enable();
+static inline void __local_end(unsigned long flags)
+{
+	migrate_enable();
 }
 
 #define __local_inc(l)		local_inc(l)
 
--

Quoted 11 lines · * Peter Zijlstra ([email protected]) wrote:

Signed-off-by Peter Zijlstra <[email protected]>

---
 include/asm-i386/local.h   |    7 ++++---
 include/asm-x86_64/local.h |    7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

Index: linux-2.6/include/asm-i386/local.h
===================================================================

include/asm-i386/local.h static __inline__ long local_sub_return( · line 200

Quoted 5 lines

include/asm-i386/local.h +1 -1

@@ -197,11 +197,12 @@ static __inline__ long local_sub_return(
 #define __local_begin(__flags)					\
 {								\
 	(__flags) = 0;						\
-	preempt_disable();					\
+	migrate_disable();					\

Brrrr. That's wrong. Your non atomic __local*() updates only makes sense when preempt_disable/enable() protects them from concurrent threads on the same CPU, which is not the case of migrate_disable/enable(). This is why I suggest that you use local_begin/end() mapped to migrate_disable/enable() for normal local variables, and, if you really want a __local_begin/end(), then it should be mapped to preempt_disable/enable() and should state that it provides no protection against interrupts.

Quoted 18 lines · Mathieu Desnoyers

Quoted 11 lines · * Peter Zijlstra ([email protected]) wrote:

Signed-off-by Peter Zijlstra <[email protected]>

---
 include/asm-i386/local.h   |    7 ++++---
 include/asm-x86_64/local.h |    7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

Index: linux-2.6/include/asm-i386/local.h
===================================================================

include/asm-i386/local.h static __inline__ long local_sub_return( · line 200

Quoted 5 lines

include/asm-i386/local.h +1 -1

@@ -197,11 +197,12 @@ static __inline__ long local_sub_return(
 #define __local_begin(__flags)					\
 {								\
 	(__flags) = 0;						\
-	preempt_disable();					\
+	migrate_disable();					\

Quoted 8 lines

Brrrr. That's wrong. Your non atomic __local*() updates only makes sense when preempt_disable/enable() protects them from concurrent threads on the same CPU, which is not the case of migrate_disable/enable(). This is why I suggest that you use local_begin/end() mapped to migrate_disable/enable() for normal local variables, and, if you really want a __local_begin/end(), then it should be mapped to preempt_disable/enable() and should state that it provides no protection against interrupts.

Sure, but on -rt it does suffice, this part of the patch is rather WIP.

Quoted 28 lines · * Peter Zijlstra ([email protected]) wrote:

Quoted 26 lines · Mathieu Desnoyers

Quoted 11 lines · * Peter Zijlstra ([email protected]) wrote:

Signed-off-by Peter Zijlstra <[email protected]>

---
 include/asm-i386/local.h   |    7 ++++---
 include/asm-x86_64/local.h |    7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

Index: linux-2.6/include/asm-i386/local.h
===================================================================

include/asm-i386/local.h static __inline__ long local_sub_return( · line 200

Quoted 5 lines

include/asm-i386/local.h +1 -1

@@ -197,11 +197,12 @@ static __inline__ long local_sub_return(
 #define __local_begin(__flags)					\
 {								\
 	(__flags) = 0;						\
-	preempt_disable();					\
+	migrate_disable();					\

Brrrr. That's wrong. Your non atomic __local*() updates only makes sense when preempt_disable/enable() protects them from concurrent threads on the same CPU, which is not the case of migrate_disable/enable(). This is why I suggest that you use local_begin/end() mapped to migrate_disable/enable() for normal local variables, and, if you really want a __local_begin/end(), then it should be mapped to preempt_disable/enable() and should state that it provides no protection against interrupts.

Quoted 3 lines

Sure, but on -rt it does suffice, this part of the patch is rather WIP.

Hrm, how can it suffice, I wonder ? migrate_disable() does not protect against other threads on the same CPU, so you could suffer from concurrent updates to the same variables. How is it different in -rt ?

Quoted 33 lines · Mathieu Desnoyers

Quoted 31 lines · * Peter Zijlstra ([email protected]) wrote:

Quoted 18 lines · Mathieu Desnoyers

Quoted 11 lines · * Peter Zijlstra ([email protected]) wrote:

Signed-off-by Peter Zijlstra <[email protected]>

---
 include/asm-i386/local.h   |    7 ++++---
 include/asm-x86_64/local.h |    7 ++++---
 2 files changed, 8 insertions(+), 6 deletions(-)

Index: linux-2.6/include/asm-i386/local.h
===================================================================

include/asm-i386/local.h static __inline__ long local_sub_return( · line 200

Quoted 5 lines

include/asm-i386/local.h +1 -1

@@ -197,11 +197,12 @@ static __inline__ long local_sub_return(
 #define __local_begin(__flags)					\
 {								\
 	(__flags) = 0;						\
-	preempt_disable();					\
+	migrate_disable();					\

Quoted 8 lines

Brrrr. That's wrong. Your non atomic __local*() updates only makes sense when preempt_disable/enable() protects them from concurrent threads on the same CPU, which is not the case of migrate_disable/enable(). This is why I suggest that you use local_begin/end() mapped to migrate_disable/enable() for normal local variables, and, if you really want a __local_begin/end(), then it should be mapped to preempt_disable/enable() and should state that it provides no protection against interrupts.

Sure, but on -rt it does suffice, this part of the patch is rather WIP.

Quoted 3 lines

Hrm, how can it suffice, I wonder ? migrate_disable() does not protect against other threads on the same CPU, so you could suffer from concurrent updates to the same variables. How is it different in -rt ?

I thought the idea was that all these local_* operation were atomic wrt to the local cpu.

The only difference with -rt is that we generally don't care about interrupts.

Anyway, I'm dropping all this local stuff, and just hard code it right into slub.c