Message-ID: <417D9371.4050305@yahoo.com.au>
Date: Tue, 26 Oct 2004 09:59:45 +1000
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: John Hawkes <hawkes@sgi.com>
CC: John Hawkes <hawkes@google.engr.sgi.com>, John Hawkes <hawkes@oss.sgi.com>,
       Ingo Molnar <mingo@elte.hu>, jbarnes@sgi.com,
       linux-kernel@vger.kernel.org, akpm@osdl.org
Subject: Re: [PATCH, 2.6.9] improved load_balance() tolerance for pinned tasks
References: <200410201936.i9KJa4FF026174@oss.sgi.com> <200410221938.MAA52152@google.engr.sgi.com> <00ee01c4b870$030b80f0$6700a8c0@comcast.net> <4179DDA3.1020405@yahoo.com.au> <001c01c4baac$056ae7d0$6700a8c0@comcast.net>
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John Hawkes wrote:

> 
> To reiterate:  this is probably reproducible on smaller SMP systems, too.
> Just do a 'runon' (using sys_sched_setaffinity) of ~200 (or more) small
> computebound processes on a single CPU.
> 

Yeah I tried that with a handful... I'll try again with 200.

> My patch -- that has load_balance() skip over (busiest->active_balance = 1)
> trigger that starts up active_load_balance() -- does seem to reduce the
> frequency of bursts of long-running activity of the migration thread, but
> those burst of activity are still there, with migration_thread consuming
> 75-95% of its CPU for several seconds (as observed by 'top').  I have not yet
> determined what's happening.  It might be an artifact of how long it takes to
> do those 'runon' startups of the computebound processes.
> 

Hmm... it would be hard to believe that it is all to do with
migrating tasks... but its possible I guess.

I'll also look into it if I can reproduce the problem here.

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