FAILED: patch "[PATCH] sched/idle/x86: Restore mwait_idle() to fix boot hangs, to" failed to apply to 3.10-stable tree

The patch below does not apply to the 3.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From: Len Brown <[email protected]>
Date: Wed, 15 Jan 2014 00:37:34 -0500
Subject: [PATCH] sched/idle/x86: Restore mwait_idle() to fix boot hangs, to
improve power savings and to improve performance

In Linux-3.9 we removed the mwait_idle() loop:

69fb3676df33 ("x86 idle: remove mwait_idle() and "idle=mwait" cmdline param")

The reasoning was that modern machines should be sufficiently happy during the boot process using the default_idle() HALT loop, until cpuidle loads and either acpi_idle or intel_idle invoke the newer MWAIT-with-hints idle loop.

But two machines reported problems:

1. Certain Core2-era machines support MWAIT-C1 and HALT only. MWAIT-C1 is preferred for optimal power and performance. But if they support just C1, cpuidle never loads and so they use the boot-time default idle loop forever.

2. Some laptops will boot-hang if HALT is used, but will boot successfully if MWAIT is used. This appears to be a hidden assumption in BIOS SMI, that is presumably valid on the proprietary OS where the BIOS was validated.

https://bugzilla.kernel.org/show_bug.cgi?id=60770

So here we effectively revert the patch above, restoring the mwait_idle() loop. However, we don't bother restoring the idle=mwait cmdline parameter, since it appears to add no value.

Maintainer notes:

For 3.9, simply revert 69fb3676df
for 3.10, patch -F3 applies, fuzz needed due to __cpuinit use in context For 3.11, 3.12, 3.13, this patch applies cleanly

index a1410db38a1a..653dfa7662e1 100644
@@ -30,6 +30,14 @@ static inline void __mwait(unsigned long eax, unsigned long ecx)
 		     :: "a" (eax), "c" (ecx));
 }
 
+static inline void __sti_mwait(unsigned long eax, unsigned long ecx)
+{
+	trace_hardirqs_on();
+	/* "mwait %eax, %ecx;" */
+	asm volatile("sti; .byte 0x0f, 0x01, 0xc9;"
+		     :: "a" (eax), "c" (ecx));
+}
+
 /*
  * This uses new MONITOR/MWAIT instructions on P4 processors with PNI,
  * which can obviate IPI to trigger checking of need_resched.

From: Len Brown <[email protected]>
Date: Wed, 15 Jan 2014 00:37:34 -0500
Subject: sched/idle/x86: Restore mwait_idle() to fix boot hangs, to improve power savings and to improve performance

In Linux-3.9 we removed the mwait_idle() loop:

69fb3676df33 ("x86 idle: remove mwait_idle() and "idle=mwait" cmdline param")

The reasoning was that modern machines should be sufficiently happy during the boot process using the default_idle() HALT loop, until cpuidle loads and either acpi_idle or intel_idle invoke the newer MWAIT-with-hints idle loop.

But two machines reported problems:

1. Certain Core2-era machines support MWAIT-C1 and HALT only. MWAIT-C1 is preferred for optimal power and performance. But if they support just C1, cpuidle never loads and so they use the boot-time default idle loop forever.

2. Some laptops will boot-hang if HALT is used, but will boot successfully if MWAIT is used. This appears to be a hidden assumption in BIOS SMI, that is presumably valid on the proprietary OS where the BIOS was validated.

https://bugzilla.kernel.org/show_bug.cgi?id=60770

So here we effectively revert the patch above, restoring the mwait_idle() loop. However, we don't bother restoring the idle=mwait cmdline parameter, since it appears to add no value.

Maintainer notes:

For 3.9, simply revert 69fb3676df
for 3.10, patch -F3 applies, fuzz needed due to __cpuinit use in context For 3.11, 3.12, 3.13, this patch applies cleanly

---
 arch/x86/kernel/process.c |   49 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

@@ -398,6 +398,52 @@ static void amd_e400_idle(void)
 		default_idle();
 }
 
+/*
+ * Intel Core2 and older machines prefer MWAIT over HALT for C1.
+ * We can't rely on cpuidle installing MWAIT, because it will not load
+ * on systems that support only C1 -- so the boot default must be MWAIT.
+ *
+ * Some AMD machines are the opposite, they depend on using HALT.
+ *
+ * So for default C1, which is used during boot until cpuidle loads,
+ * use MWAIT-C1 on Intel HW that has it, else use HALT.
+ */
+static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
+{
+	if (c->x86_vendor != X86_VENDOR_INTEL)
+		return 0;
+
+	if (!cpu_has(c, X86_FEATURE_MWAIT))
+		return 0;
+
+	return 1;
+}
+
+/*
+ * MONITOR/MWAIT with no hints, used for default default C1 state.
+ * This invokes MWAIT with interrutps enabled and no flags,
+ * which is backwards compatible with the original MWAIT implementation.
+ */
+
+static void mwait_idle(void)
+{
+	if (!current_set_polling_and_test()) {
+		if (static_cpu_has(X86_FEATURE_CLFLUSH_MONITOR)) {
+			mb();
+			clflush((void *)&current_thread_info()->flags);
+			mb();
+		}
+
+		__monitor((void *)&current_thread_info()->flags, 0, 0);
+		if (!need_resched())
+			__sti_mwait(0, 0);
+		else
+			local_irq_enable();
+	} else
+		local_irq_enable();
+	__current_clr_polling();
+}
+
 void __cpuinit select_idle_routine(const struct cpuinfo_x86 *c)
 {
 #ifdef CONFIG_SMP

@@ -411,6 +457,9 @@ void __cpuinit select_idle_routine(const
 		/* E400: APIC timer interrupt does not wake up CPU from C1e */
 		pr_info("using AMD E400 aware idle routine\n");
 		x86_idle = amd_e400_idle;
+	} else if (prefer_mwait_c1_over_halt(c)) {
+		pr_info("using mwait in idle threads\n");
+		x86_idle = mwait_idle;
 	} else
 		x86_idle = default_idle;
 }

Thanks, now applied.

greg k-h