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

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Message-ID: <20090911075832.GG18599@kernel.dk>
Date:	Fri, 11 Sep 2009 09:58:32 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Ingo Molnar <mingo@...e.hu>
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

On Fri, Sep 11 2009, Ingo Molnar wrote:
> 
> * 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.

Yes

> 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.

I did, it's a simple 'generate random data and compress it' work piece
for each client. You can control the amount of work with -x, which sets
the kb of data it'll work on. Stats are generated both for wakeup
latency, and work processing latency.

-- 
Jens Axboe

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