Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets - bisected

Ingo Molnar
2012-09-27T06:41:48Z

* Mike Galbraith <efault@gmx.de> wrote:

> > Just to confirm, if you turn off all preemption via a hack
> > (basically if you turn SCHED_OTHER into SCHED_BATCH), does
> > psql perform and scale much better, with the quality of
> > sibling selection and spreading of processes only being a
> > secondary effect?
>
> That has always been the case here. Preemption dominates.

Yes, so we get the best psql performance if we allow the central
proxy process to dominate a single CPU (IIRC it can easily go up
to 100% CPU utilization on that CPU - it is what determines max
psql throughput), and not let any worker run there much, right?

> Others should play with it too, and let their boxen speak.

Do you have an easy-to-apply hack patch by chance that has the
effect of turning off all such preemption, which people could
try?

Thanks,

Ingo