linux-kernel - Re: [long] Another BFS versus CFS shakedown

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Message-ID: <20090911075331.GA14489@elte.hu>
Date:	Fri, 11 Sep 2009 09:53:31 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	Frans Pop <elendil@...net.nl>, linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [long] Another BFS versus CFS shakedown

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

> On Fri, Sep 11 2009, Frans Pop wrote:
> > On Friday 11 September 2009, Ingo Molnar wrote:
> > > Note, the one you used was a still buggy version of latt.c producing
> > > bogus latency numbers - you will need the fix to it attached below.
> > 
> > Yes, I'm aware of that and have already copied Jens' latest version.
> 
> BTW, I put it in a git repo, it quickly gets really confusing with so
> many version going around. So that can be accessed here:
> 
> git://git.kernel.dk/latt.git
> 
> and as with my other repos, snapshots are automatically generated every
> hour when new commits have been made. To get the very latest latt and
> not have to use git, download:
> 
> http://brick.kernel.dk/snaps/latt-git-latest.tar.gz

Btw., your earlier latt reports should be discarded as invalid due 
to that bug.

With the fixed latt.c version the mainline latencies (both 
worst-case and average) were reported to be better after the poll() 
bug got fixed, so in that area, for this kind of measurement, 
mainline seems to be working well.

[ What happened is that the poll() bug was creating false latencies
  in the mainline scheduler tests. (BFS avoided measuring that bug
  incidentally, by its agressive balancer moved the wakee tasks away
  from the buggy busy-looping poll() looping parent task. Two
  instances of latt.c would possibly have shown similar latencies.) ]

I see you added new 'work generator' changes to latt.c now, will 
check/validate that version of latt.c too.

Thanks,

	Ingo
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