Re: [PATCH] Performance regression in 2.6.7-rc3

[Con Kolivas <kernel@kolivas.org>]

Quoting Nick Piggin <nickpiggin@yahoo.com.au>:
> Ingo Molnar wrote:
> >* Con Kolivas <kernel@kolivas.org> wrote:
> >>with a little bit of detective work and help from Wli we tracked down that
> 
> >>this patch caused it:
> >>[PATCH] sched: improve wakeup-affinity
> >>
> >
> >>A massive increase in idle time was observed and the throughput
> >>dropped by 40% Reversing this patch gave these results:
> >>
> >
> >>backsched1: http://khack.osdl.org/stp/293865/
> >>Composite 	Query Processing Power 	Throughput Numerical Quantity
> >>193.93 	145.95 	257.67
> >>
> >>It may be best to reverse this patch until the regression is better 
> >>understood.
> >agreed. It is weird because Nick said that pgsql was tested with the
> >patch - and we applied the patch based on those good results. Nick?
> Sigh, yes, Mark did run a test for me, but I think it was dbt2-pgsql.
> This one is dbt3-pgsql. Also, his system was a 4 logical CPU Xeon.
> 
> Strangely enough, Mark's setup was showing a fairly large too-much-idle
> regression not long ago, while these 8-ways weren't.
> 
> Anyway, Linus has reverted my patch now, which is the right thing to
> do. Your sync wakeup change is still in there, so that will hopefully
> help bw_pipe scores.

The sync wakeup change was worth about 1% detriment to this benchmark which, if
offset by significant performance gains elsewhere, is worth tolerating.

Con