linux-kernel - Re: [patch] CFS scheduler, -v8

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Date:	Wed, 2 May 2007 12:05:45 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Balbir Singh <balbir@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Peter Williams <pwil3058@...pond.net.au>,
	Thomas Gleixner <tglx@...utronix.de>, caglar@...dus.org.tr,
	Willy Tarreau <w@....eu>,
	Gene Heskett <gene.heskett@...il.com>, Mark Lord <lkml@....ca>,
	Zach Carter <linux@...hcarter.com>,
	buddabrod <buddabrod@...il.com>
Subject: Re: [patch] CFS scheduler, -v8


* Balbir Singh <balbir@...ux.vnet.ibm.com> wrote:

> With -v7 I would run the n/n+1 test. Basically on a system with n 
> cpus, I would run n+1 tasks and see how their load is distributed. I 
> usually find that the last two tasks would get stuck on one CPU on the 
> system and would get half the cpu time as their other peers. I think 
> this issue has been around for long even before CFS. But while I was 
> investigating that, I found that with -v8, all the n+1 tasks are stuck 
> on the same cpu.

i believe this problem is specific to powerpc - load is distributed fine 
on i686/x86_64 and your sched_debug shows a cpu_load[0] == 0 on CPU#2 
which is 'impossible'. (I sent a few suggestions off-Cc about how to 
debug this.)

	Ingo
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