linux-kernel - Re: BFS vs. mainline scheduler benchmarks and measurements

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Date:	Wed, 9 Sep 2009 08:13:08 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Con Kolivas <kernel@...ivas.org>, linux-kernel@...r.kernel.org,
	Mike Galbraith <efault@....de>
Subject: Re: BFS vs. mainline scheduler benchmarks and measurements


* Jens Axboe <jens.axboe@...cle.com> wrote:

> On Tue, Sep 08 2009, Peter Zijlstra wrote:
> > On Tue, 2009-09-08 at 11:13 +0200, Jens Axboe wrote:
> > > And here's a newer version.
> > 
> > I tinkered a bit with your proglet and finally found the 
> > problem.
> > 
> > You used a single pipe per child, this means the loop in 
> > run_child() would consume what it just wrote out until it got 
> > force preempted by the parent which would also get woken.
> > 
> > This results in the child spinning a while (its full quota) and 
> > only reporting the last timestamp to the parent.
> 
> Oh doh, that's not well thought out. Well it was a quick hack :-) 
> Thanks for the fixup, now it's at least usable to some degree.

What kind of latencies does it report on your box?

Our vanilla scheduler default latency targets are:

  single-core: 20 msecs
    dual-core: 40 msecs
    quad-core: 60 msecs
    opto-core: 80 msecs

You can enable CONFIG_SCHED_DEBUG=y and set it directly as well via 
/proc/sys/kernel/sched_latency_ns:

   echo 10000000 > /proc/sys/kernel/sched_latency_ns

	Ingo
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