Patch "x86 idle: Repair large-server 50-watt idle-power regression" has been added to the 3.12-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    x86 idle: Repair large-server 50-watt idle-power regression

to the 3.12-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-idle-repair-large-server-50-watt-idle-power-regression.patch
and it can be found in the queue-3.12 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 40e2d7f9b5dae048789c64672bf3027fbb663ffa Mon Sep 17 00:00:00 2001
From: Len Brown <len.brown@xxxxxxxxx>
Date: Wed, 18 Dec 2013 16:44:57 -0500
Subject: x86 idle: Repair large-server 50-watt idle-power regression

From: Len Brown <len.brown@xxxxxxxxx>

commit 40e2d7f9b5dae048789c64672bf3027fbb663ffa upstream.

Linux 3.10 changed the timing of how thread_info->flags is touched:

	x86: Use generic idle loop
	(7d1a941731fabf27e5fb6edbebb79fe856edb4e5)

This caused Intel NHM-EX and WSM-EX servers to experience a large number
of immediate MONITOR/MWAIT break wakeups, which caused cpuidle to demote
from deep C-states to shallow C-states, which caused these platforms
to experience a significant increase in idle power.

Note that this issue was already present before the commit above,
however, it wasn't seen often enough to be noticed in power measurements.

Here we extend an errata workaround from the Core2 EX "Dunnington"
to extend to NHM-EX and WSM-EX, to prevent these immediate
returns from MWAIT, reducing idle power on these platforms.

While only acpi_idle ran on Dunnington, intel_idle
may also run on these two newer systems.
As of today, there are no other models that are known
to need this tweak.

Link: http://lkml.kernel.org/r/CAJvTdK=%2BaNN66mYpCGgbHGCHhYQAKx-vB0kJSWjVpsNb_hOAtQ@xxxxxxxxxxxxxx
Signed-off-by: Len Brown <len.brown@xxxxxxxxx>
Link: http://lkml.kernel.org/r/baff264285f6e585df757d58b17788feabc68918.1387403066.git.len.brown@xxxxxxxxx
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 arch/x86/kernel/cpu/intel.c |    3 ++-
 drivers/idle/intel_idle.c   |    3 +++
 2 files changed, 5 insertions(+), 1 deletion(-)

--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -387,7 +387,8 @@ static void init_intel(struct cpuinfo_x8
 			set_cpu_cap(c, X86_FEATURE_PEBS);
 	}
 
-	if (c->x86 == 6 && c->x86_model == 29 && cpu_has_clflush)
+	if (c->x86 == 6 && cpu_has_clflush &&
+	    (c->x86_model == 29 || c->x86_model == 46 || c->x86_model == 47))
 		set_cpu_cap(c, X86_FEATURE_CLFLUSH_MONITOR);
 
 #ifdef CONFIG_X86_64
--- a/drivers/idle/intel_idle.c
+++ b/drivers/idle/intel_idle.c
@@ -361,6 +361,9 @@ static int intel_idle(struct cpuidle_dev
 
 	if (!current_set_polling_and_test()) {
 
+		if (this_cpu_has(X86_FEATURE_CLFLUSH_MONITOR))
+			clflush((void *)&current_thread_info()->flags);
+
 		__monitor((void *)&current_thread_info()->flags, 0, 0);
 		smp_mb();
 		if (!need_resched())


Patches currently in stable-queue which might be from len.brown@xxxxxxxxx are

queue-3.12/x86-idle-repair-large-server-50-watt-idle-power-regression.patch
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