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SubjectRe: [Patch] Scale pidhash_shift/pidhash_size up based on num_possible_cpus().
On Fri, Aug 01, 2008 at 11:27:20AM -0700, Eric W. Biederman wrote:
> Robin Holt <holt@sgi.com> writes:
>
> > On Thu, Jul 31, 2008 at 03:04:56PM -0700, Eric W. Biederman wrote:
> >> Robin Holt <holt@sgi.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?

Oops, confusing details. That was a different problem we had been
tracking.

Sorry for the confusion,
Robin


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