Messages in this thread | | | Date | Mon, 14 Dec 2009 17:49:16 +0000 | From | James Pearson <> | Subject | Re: High load average on idle machine running 2.6.32 |
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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@chello.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@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.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
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