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

Ingo Molnar
2007-07-31T08:57:36Z

* Peter Zijlstra <peterz@infradead.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