linux-kernel - Re: 2.6.21-rc3-mm1 RSDL results

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Message-ID: <20070309215716.GK943@1wt.eu>
Date:	Fri, 9 Mar 2007 22:57:17 +0100
From:	Willy Tarreau <w@....eu>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Con Kolivas <kernel@...ivas.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org
Subject: Re: 2.6.21-rc3-mm1 RSDL results

On Fri, Mar 09, 2007 at 03:39:59PM -0600, Matt Mackall wrote:
> On Sat, Mar 10, 2007 at 08:19:18AM +1100, Con Kolivas wrote:
> > On Saturday 10 March 2007 08:07, Con Kolivas wrote:
> > > On Saturday 10 March 2007 07:46, Matt Mackall wrote:
> > > > My suspicion is the problem lies in giving too much quanta to
> > > > newly-started processes.
> > >
> > > Ah that's some nice detective work there. Mainline does some rather complex
> > > accounting on sched_fork including (possibly) a whole timer tick which rsdl
> > > does not do. make forks off continuously so what you say may well be
> > > correct. I'll see if I can try to revert to the mainline behaviour in
> > > sched_fork (which was obviously there for a reason).
> > 
> > Wow! Thanks Matt. You've found a real bug too. This seems to fix the qemu
> >  misbehaviour and bitmap errors so far too! Now can you please try this to see
> >  if it fixes your problem?
> 
> Sorry, it's about the same. I now suspect an accounting glitch involving
> pipe wake-ups.
> 
> 5x memload: good
> 5x execload: good
> 5x forkload: good
> 5 parallel makes: mostly good
> make -j 5: bad
> 
> So what's different between makes in parallel and make -j 5? Make's
> job server uses pipe I/O to control how many jobs are running.

Matt, could you check with plain 2.6.20 + Con's patch ? It is possible
that he added bugs when porting to -mm, or that someting in -mm causes
the trouble. Your experience with -mm seems so much different from mine
with mainline, there must be a difference somewhere !

Con, is your patch necessary for mainline patch too ? I see that it
should apply, but sometimes -mm may justify changes.

Best regards,
Willy

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