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

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Date:	Fri, 9 Mar 2007 15:39:59 -0600
From:	Matt Mackall <mpm@...enic.com>
To:	Con Kolivas <kernel@...ivas.org>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	akpm@...ux-foundation.org
Subject: Re: 2.6.21-rc3-mm1 RSDL results

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.

-- 
Mathematics is the supreme nostalgia of our time.
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