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

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Message-ID: <20070310004948.GN10394@waste.org>
Date:	Fri, 9 Mar 2007 18:49:48 -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 11:34:26AM +1100, Con Kolivas wrote:
> On Saturday 10 March 2007 09:29, Matt Mackall wrote:
> > On Sat, Mar 10, 2007 at 09:18:05AM +1100, Con Kolivas wrote:
> > > On Saturday 10 March 2007 08:57, Con Kolivas wrote:
> > > > On Saturday 10 March 2007 08:39, 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.
> > > >
> > > > Hmm it must be those deep pipes again then. I removed any quirks
> > > > testing for those from mainline as I suspected it would be ok. Guess
> > > > I"m wrong.
> > >
> > > I shouldn't blame this straight up though if NO_HZ makes it better.
> > > Something else is going wrong... wtf though?
> >
> > Just so we're clear, dynticks has only 'fixed' the single non-parallel
> > make load so far.
> 
> Ok, so some of the basics then. Can you please give me the output of 'top -b' 
> running for a few seconds during the whole affair?

Here you go:

http://selenic.com/baseline
http://selenic.com/underload
 
This is with 2.6.20+rsdl+tickfix at HZ=250.

Something I haven't mentioned about my setup is that I'm using ccache.
And it turns out disabling ccache makes a large difference. Going to
switch back to a NO_HZ kernel and see what that looks like.

-- 
Mathematics is the supreme nostalgia of our time.
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