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Message-ID: <m1proszj3r.fsf@frodo.ebiederm.org>
Date: Fri, 01 Aug 2008 11:27:20 -0700
From: ebiederm@...ssion.com (Eric W. Biederman)
To: Robin Holt <holt@....com>
Cc: linux-kernel@...r.kernel.org, Pavel Emelyanov <xemul@...nvz.org>,
Oleg Nesterov <oleg@...sign.ru>,
Sukadev Bhattiprolu <sukadev@...ibm.com>,
Paul Menage <menage@...gle.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Patch] Scale pidhash_shift/pidhash_size up based on num_possible_cpus().
Robin Holt <holt@....com> writes:
> On Thu, Jul 31, 2008 at 03:04:56PM -0700, Eric W. Biederman wrote:
>> Robin Holt <holt@....com> writes:
>>
>> > Like so???
>> >
>> > I have not tested this yet.
>>
>> Looks reasonable to me.
>>
>> In what circumstances was the lookup in the pid hash table with
>> long changes causing a performance slowdown?. We don't perform
>> a lot of lookups.
>
> It was initially detected while profiling 'ps' on a 2048p machine that
> had 13 kernel threads per cpu. We added a couple more device drivers
> which added additional threads. We then started a pthread-on-process
> MPI job which had 2048 ranks each with 4 threads (test-case from
> customer job). There were misc other processes out there which brought
> our task count up to approx 63k. Larger page size helped the problem
> (went from 16k to 64k).
Large page size? Do you mean larger hash size?
What were you measuring that showed improvement with the large hash size?
Eric
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