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Date: Fri, 18 Dec 2009 14:43:56 +0100 From: Andrea Suisani <sickpig@...nioni.net> To: James Pearson <james-p@...ing-picture.com> CC: linux-kernel@...r.kernel.org, Peter Zijlstra <a.p.zijlstra@...llo.nl> Subject: Re: High load average on idle machine running 2.6.32 [cc:ed Peter Zijlstra] James Pearson wrote: > James Pearson wrote: > >>> I've booted a 64 bit 2.6.32 kernel on dual processor, quad core Xeon >>> E5440 machine. The load average when the machine is idle varies >>> between 2 and 3. >>> >>> When using a 2.6.31 kernel on the same machine, the load average when >>> idle is nearly 0 >>> >>> The kernel doesn't use modules - all that is needed is compiled in. >>> The machine uses NFS-root >>> >>> Strangely, when I run 'iftop' (from >>> http://www.ex-parrot.com/pdw/iftop/) using the 2.6.32 kernel, the >>> load average drops to below 0.5 - stop running iftop, and the load >>> average climbs again ... >>> >>> Any idea what might be causing this? >> >> >> It looks like whatever is causing this happened between 2.6.31-git7 >> and 2.6.31-git8 - unfortunately I don't know how to find out what >> change caused this ... >> >> Also, if I 'hot-unplug' CPUs 1 to 7, the load average drops to 0 - >> when I re-enable theses CPUs, the load average climbs. >> >> I guess this is a problem with my particular config - or maybe because >> I'm using NFS-root (the root file system is readonly), or using a >> non-module kernel? > > I gave 'git bisect' a go - which appears to suggest that my problem > started at: > > % git bisect bad > d7c33c4930f569caf6b2ece597432853c4151a45 is first bad commit > commit d7c33c4930f569caf6b2ece597432853c4151a45 > Author: Peter Zijlstra <a.p.zijlstra@...llo.nl> > Date: Fri Sep 11 12:45:38 2009 +0200 > > sched: Fix task affinity for select_task_rq_fair > > While merging select_task_rq_fair() and sched_balance_self() I made > a mistake that leads to testing the wrong task affinty. > > Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl> > LKML-Reference: <new-submission> > Signed-off-by: Ingo Molnar <mingo@...e.hu> > > :040000 040000 3d7aa3e193c7faf9c7ebbb1443c6f63269d86d04 > 9cfb647eb5d80f156fd8a495da68f765c3fdd772 M kernel > > > However, while running the bisects, it became harder to decide what was > a 'bad' and a 'good' idle load average - for example the kernel with the > above patch gave an idle load average of about 1.5 - which is not as > high as the idle load average seen with a 2.6.32 kernel and the kernel > without this patch gave an idle load average of about 0.7 - which is not > as low as the idle load average with a 2.6.31 kernel ... > > So I guess, it is not just one patch that has caused the issue I'm > seeing, which I guess is to be expected as the above patch was part of > the 'scheduler updates for v2.6.32' patch set > <http://marc.info/?l=linux-kernel&m=125322428306777&w=2> > > I guess as no one else has reported this issue - it must be something to > do with my set up - could using NFS-root affect how the load average is > calculated? > > Or, do I have something strange or missing in my kernel config that > could cause this issue? > > Thanks > > James Pearson > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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