linux-kernel - Re: x264 benchmarks BFS vs CFS

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Message-Id: <1261056647.10838.26.camel@marge.simson.net>
Date:	Thu, 17 Dec 2009 14:30:47 +0100
From:	Mike Galbraith <efault@....de>
To:	Kasper Sandberg <lkml@...anurb.dk>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Jason Garrett-Glaser <darkshikari@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML Mailinglist <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: x264 benchmarks BFS vs CFS

On Thu, 2009-12-17 at 12:00 +0100, Kasper Sandberg wrote:
> On Thu, 2009-12-17 at 11:53 +0100, Ingo Molnar wrote:
> > * Jason Garrett-Glaser <darkshikari@...il.com> wrote:
> > 
> > > On Thu, Dec 17, 2009 at 1:33 AM, Kasper Sandberg <lkml@...anurb.dk> wrote:
> > > > well well :) nothing quite speaks out like graphs..
> > > >
> > > > http://doom10.org/index.php?topic=78.0
> > > >
> > > >
> > > >
> > > > regards,
> > > > Kasper Sandberg
> > > 
> > > Yeah, I sent this to Mike a bit ago.  Seems that .32 has basically tied 
> > > it--and given the strict thread-ordering expectations of x264, you basically 
> > > can't expect it to do any better, though I'm curious what's responsible for 
> > > the gap in "veryslow", even with SCHED_BATCH enabled.
> > > 
> > > The most odd case is that of "ultrafast", in which CFS immediately ties BFS 
> > > when we enable SCHED_BATCH.  We're doing some further testing to see exactly 
> 
> Thats kinda besides the point.
> 
> all these tunables and weirdness is _NEVER_ going to work for people.

Fact is, it is working for a great number of people, the vast majority
of whom don't even know where the knobs are, much less what they do. 

> now forgive me for being so blunt, but for a user, having to do
> echo x264 > /proc/cfs/gief_me_performance_on_app
> or
> echo some_benchmark > x264 > /proc/cfs/gief_me_performance_on_app

Theatrics noted.

> just isnt usable, bfs matches, even exceeds cfs on all accounts, with
> ZERO user tuning, so while cfs may be able to nearly match up with a ton
> of application specific stuff, that just doesnt work for a normal user.

Seems you haven't done much benchmarking.  BFS has strengths as well as
weaknesses, all schedulers do.

> not to mention that bfs does this whilst not loosing interactivity,
> something which cfs certainly cannot boast.

Not true.  I sent Con hard evidence of a severe problem area wrt
interactivity, and hard numbers showing other places where BFS needs
some work.  But hey, if BFS blows your skirt up, use it and be happy.

	-Mike

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