FAILED: patch "[PATCH] sched/idle/x86: Restore mwait_idle() to fix boot hangs, to" failed to apply to 3.14-stable tree

The patch below does not apply to the 3.14-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/include/asm/mwait.h |    8 ++++++
 arch/x86/kernel/process.c    |   50 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 58 insertions(+)

@@ -30,6 +30,14 @@ static inline void __mwait(unsigned long
 		     :: "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.

Thanks, now applied.

greg k-h

[...]

Thanks! I'll use this backport for the 3.16 kernel as well.

Cheers,
--
Lu�s