Re: SMP performance degradation with sysbench

[Nick Piggin]

Nick Piggin wrote:
> Rik van Riel wrote:
>
> > Lorenzo Allegrucci wrote:
> >
> > > Hi lkml,
> > >
> > > according to the test below (sysbench) Linux seems to have scalability
> > > problems beyond 8 client threads:
> > > http://jeffr-tech.livejournal.com/6268.html#cutid1
> > > http://jeffr-tech.livejournal.com/5705.html
> > > Hardware is an 8-core amd64 system and jeffr seems willing to try more
> > > Linux versions on that machine.
> > > Anyway, is there anyone who can reproduce this?
> >
> >
> >
> > I have reproduced it on a quad core test system.
> >
> > With 4 threads (on 4 cores) I get a high throughput, with
> > approximately 58% user time and 42% system time.
> >
> > With 8 threads (on 4 cores) I get way lower throughput,
> > with 37% user time, 29% system time 35% idle time!
> >
> > The maximum time taken per query also increases from
> > 0.0096s to 0.5273s. Ouch!
> >
> > I don't know if this is MySQL, glibc or Linux kernel,
> > but something strange is going on...
>
>
> Like you, I'm also seeing idle time start going up as threads increase.
>
> I initially thought this was a problem with the multiprocessor scheduler,
> because the pattern is exactly like some artificat in the load balancing.

"artificat"

Wow. I must need some sleep :) Please excuse any other typos!

--
SUSE Labs, Novell Inc.
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