Re: [git pull] scheduler fixes

Mike Galbraith
2009-01-17T16:37:29Z

On Sat, 2009-01-17 at 17:25 +0100, Ingo Molnar wrote:
> * Mike Galbraith <efault@gmx.de> wrote:
>
> > On Sat, 2009-01-17 at 17:01 +0100, Ingo Molnar wrote:
> > > * Mike Galbraith <efault@gmx.de> wrote:
> > >
> > > > On Sat, 2009-01-17 at 04:43 -0800, Andrew Morton wrote:
> > > > > http://bugzilla.kernel.org/show_bug.cgi?id=12465 just popped up - another
> > > > > scheduler regression. It has been bisected.
> > > >
> > > > Seems pretty clear. I'd suggest reverting it.
> > >
> > > We can revert it (and will revert it if no solution is found), but i'd
> > > also like to understand why it happens, because that kind of
> > > regression from this change is unexpected - we might be hiding some
> > > bug that could pop up under less debuggable circumstances, so we need
> > > to understand it while we have a chance.
> >
> > Agree. However, with the sched_mc stuff, mysql+oltp now does better
> > with NEWIDLE on than off as well, as does an nfs kbuild.
>
> Didnt you come up with the verdict that sched_mc=2 is not a win - or has
> that changed? If we should change the defaults then please send a
> re-tuning patch against the latest code.

sched_mc=2 was better than sched_mc=1. The other balancing changes put
a dent in mysql+oltp peak and immediately after peak. Setting
sched_mc=2 brought back the loss that was otherwise there all the way
through the curve back to 28 level, so with sched_mc=2, there was only
the slight loss of peak, and larger loss of post-peak.

> Still, the ping delays of multiple seconds are completely unacceptable and
> need to be understood, or these will come back and might bite us in a lot
> less fortunate place. NEWIDLE and WAKE_BALANCE has micro-effects on
> latencies - anything in the user-visible range is highly anomalous at
> these low load levels.
>
> Ingo