Re: SMP performance degradation with sysbench

[Rik van Riel <riel@redhat.com>]

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...

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