lkml.org 
[lkml]   [2008]   [May]   [14]   [last100]   RSS Feed
Views: [more markup]  [less markup]  [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
DateWed, 14 May 2008 08:56:05 +0200
FromIngo Molnar <>
SubjectRe: [BISECTED] Lots of "rescheduling IPIs" in powertop
* Vegard Nossum <vegard.nossum@gmail.com> wrote:

> Hi,
> 
> Recap: powertop shows between 200-400 wakeups/second with the 
> description "<kernel IPI>: Rescheduling interrupts" when all 
> processors have load (e.g. I need to run two busy-loops on my 2-CPU 
> system for this to show up).

ok, could you try the fix below? It was a mistake to make mwait use 
dependent on power considerations - on a desktop CPU it is unlikely to 
use more power than a simple HLT - and the IPIs are extra scheduling 
latency and extra power used.

	Ingo

-------------->
Subject: x86: remove mwait C-state capability
From: Ingo Molnar <mingo@elte.hu>
Date: Wed May 14 08:47:40 CEST 2008
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 arch/x86/kernel/process.c |   11 +----------
 1 file changed, 1 insertion(+), 10 deletions(-)
Index: linux/arch/x86/kernel/process.c
===================================================================
--- linux.orig/arch/x86/kernel/process.c
+++ linux/arch/x86/kernel/process.c
@@ -99,15 +99,6 @@ static void mwait_idle(void)
 		local_irq_enable();
 }
 
-
-static int __cpuinit mwait_usable(const struct cpuinfo_x86 *c)
-{
-	if (force_mwait)
-		return 1;
-	/* Any C1 states supported? */
-	return c->cpuid_level >= 5 && ((cpuid_edx(5) >> 4) & 0xf) > 0;
-}
-
 /*
  * On SMP it's slightly faster (but much more power-consuming!)
  * to poll the ->work.need_resched flag instead of waiting for the
@@ -131,7 +122,7 @@ void __cpuinit select_idle_routine(const
 			" performance may degrade.\n");
 	}
 #endif
-	if (cpu_has(c, X86_FEATURE_MWAIT) && mwait_usable(c)) {
+	if (cpu_has(c, X86_FEATURE_MWAIT)) {
 		/*
 		 * Skip, if setup has overridden idle.
 		 * One CPU supports mwait => All CPUs supports mwait

\
 
 \ /
  Last update: 2008-05-14 08:59    [from the cache]
©2003-2008