linux-kernel - Re: [RFC patch 1/2] sched: dynamically adapt granularity with nr

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Date:	Sun, 12 Sep 2010 14:16:26 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Mike Galbraith <efault@....de>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tony Lindgren <tony@...mide.com>
Subject: Re: [RFC patch 1/2] sched: dynamically adapt granularity with
	nr_running

* Mike Galbraith (efault@....de) wrote:
> On Sun, 2010-09-12 at 08:14 +0200, Ingo Molnar wrote:
> > * Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:
> > 
> > > (on a uniprocessor 2.0 GHz Pentium M)
> > > 
> > > * Without the patch:
> > > 
> > >  - wakeup-latency with SIGEV_THREAD in parallel with youtube video and
> > >    make -j10
> > > 
> > > maximum latency: 50107.8 µs
> > > average latency: 6609.2 µs
> > > missed timer events: 0
> > 
> > I tried your patches on a similar UP system, using wakeup-latency.c. I 
> > also measured the vanilla upstream kernel (cced86a) with the default 
> > granularity settings, and also vanilla with a sched_min_granularity/3 
> > tune (patch attached below for that).
> > 
> > I got the following results (make -j10 kbuild load, average of 3 runs):
> > 
> >  vanilla: 
> > 
> >   maximum latency: 38278.9 µs
> >   average latency:  7730.1 µs
> > 
> >  mathieu-dyn:
> > 
> >   maximum latency: 28698.8 µs
> >   average latency:  7757.1 µs
> > 
> >  peterz-min_gran/3:
> > 
> >   maximum latency: 22702.1 µs
> >   average latency:  6684.8 µs
> 
> One thing that springs to mind with make is that it does vfork, so kinda
> sorta continues running in drag, so shouldn't get credit for sleeping,
> as that introduces bogus spread.  Post vfork parent notification time
> adjustment may suffice, think I'll try that.

Hrm, I might be misunderstanding what you are saying here, but when a new
process/thread is forked and woken up, we fall in the "initial" case of
place_entity, so we increase the vruntime of a whole slice rather than getting
credit for sleeping.

Or am I missing your point ?

Thanks,

Mathieu

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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