Re: 2.6.21-rc3-mm1 RSDL results

Matt Mackall
2007-03-09T22:32:50Z

On Sat, Mar 10, 2007 at 09:12:07AM +1100, Con Kolivas wrote:
> On Saturday 10 March 2007 08:57, Willy Tarreau wrote:
> > 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 !
>
> Good idea.

2.6.20+RSDL+tickfix+noyield behaves more or less the same under make
-j5 as 2.6.21-rc3-mm1. A bit worse, perhaps. There's no tickless on
2.6.20, so that could explain that.

--
Mathematics is the supreme nostalgia of our time.