Message-ID: <4414F911.4060807@bigpond.net.au>
Date: Mon, 13 Mar 2006 15:46:09 +1100
From: Peter Williams <pwil3058@bigpond.net.au>
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To: Andrew Morton <akpm@osdl.org>
CC: linux-kernel@vger.kernel.org, Con Kolivas <kernel@kolivas.org>,
       "Chen, Kenneth W" <kenneth.w.chen@intel.com>,
       John Hawkes <hawkes@sgi.com>, Ingo Molnar <mingo@elte.hu>,
       npiggin@suse.de, "Siddha, Suresh B" <suresh.b.siddha@intel.com>
Subject: Re: 2.6.16-rc5-mm1 -- strange load balancing problems
References: <20060228042439.43e6ef41.akpm@osdl.org> <4406C881.3060400@bigpond.net.au> <4407706D.90604@bigpond.net.au>
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Peter Williams wrote:
> Peter Williams wrote:
> 
>> I'm seeing some strange load balancing problems with this kernel.  I 
>> don't think that they're due to the smpnice patches as I've applied 
>> them on a standard 2.6.15-rc5 kernel and the problem doesn't happen 
>> there.
>>
>> The problem is (as I say) quite strange and (for me) very 
>> reproducible.  I have two programs (aspin and gsmiley) which I use to 
>> produce CPU hard spinners for testing purposes.  What I'm finding is 
>> that when I start several copies of aspin load balancing goes as 
>> expected but when I launch several copies of gsmiley they all go to 
>> the one CPU and stick there like glue.  (The most obvious difference 
>> between the two programs is that aspin is just a command line tool 
>> while gsmiley is an X windows program that spins a simley face and 
>> reports its own assessment of the percentage of CPU it's getting.)  
>> The machine that I've seen this problem is a hyper threading Pentium 4 
>> and I suspect that it may be due to the SCHED_MC changes which overlap 
>> SCHED_SMT a bit.
>>
>> I'm trying to test this on a non hyper threading machine but the 
>> machine has crashed (different kernel) while doing the build.  I'll 
>> resume this effort tomorrow but I thought that I should report the 
>> problem so that others could comment.
>>
>> Peter
>> PS SCHED_MC was configured in but I'll try it without tomorrow and 
>> report the results.
> 
> 
> Configuring SCHED_MC to "no" causes this problem to go away.

This problem does not appear to be present in 2.6.16-rc6-mm1.

Peter
-- 
Peter Williams                                   pwil3058@bigpond.net.au

"Learning, n. The kind of ignorance distinguishing the studious."
  -- Ambrose Bierce
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