linux-kernel - Re: SD still better than CFS for 3d ?(was Re: 2.6.23-rc1)

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Date:	Tue, 31 Jul 2007 10:57:13 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Kasper Sandberg <lkml@...anurb.dk>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	ck@....kolivas.org
Subject: Re: SD still better than CFS for 3d   ?(was Re: 2.6.23-rc1)


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, 2007-07-31 at 01:46 +0200, Kasper Sandberg wrote:
> 
> > could perhaps be filesystem related, i have my maildir(extremely 
> > large) on reiserfs, and /home on xfs. what my mail client will do is 
> > download mail, spamasassin it(loading database from home), then it 
> > will put to imap server placing it on reiserfs, and then a "local" 
> > copy in my home.
> 
> Ooh, do you perchance have PREEMPT_BKL=y?
> 
> If so, try on another filesystem than reiserfs (or disable 
> PREEMPT_BKL, but that is obviously the lesser of the two choices).
> 
> Ingo traced a 1+ second latency at my end to BKL priority inversion 
> between tty and reiserfs.

ah, indeed, that makes quite a bit of sense. Almost all of the Reiser3 
code runs under the BKL, and the only other major kernel infrastructure 
that has BKL dependencies is the TTY code. Kasper, as a debugging 
matter, could you try to move that spamassassin workload off into a 
non-Reiser3 filesystem and/or disable PREEMPT_BKL? If that makes a 
noticeable difference (for the better ;) then we can continue figuring 
out what's happening exactly.

	Ingo
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