Re: [PATCH 0/4] pending scheduler updates

From: Mike Galbraith
Date: Wed Oct 22 2008 - 13:57:24 EST

On Wed, 2008-10-22 at 19:38 +0200, Peter Zijlstra wrote:
> On Wed, 2008-10-22 at 12:32 +0200, Mike Galbraith wrote:
> > On Wed, 2008-10-22 at 12:03 +0200, Mike Galbraith wrote:
> >
> > > It has positive effects too, but IMHO, the bad outweigh the good.
> >
> > BTW, most dramatic on the other end of the spectrum is pgsql+oltp. With
> > preemption as is, it collapses as load climbs to heavy with preemption
> > knobs at stock. Postgres uses user-land spinlocks and _appears_ to wake
> > others while these are still held. For this load, there is such a thing
> > as too much short-term fairness, preempting lock holder creates nasty
> > gaggle of contended lock spinners. It's curable with knobs, and I think
> > it's postgres's own fault, but may be wrong.
> >
> > With that patch, pgsql+oltp scales perfectly.
> Are we talking about this patch, which re-instates the vruntime based
> wakeup-preemption ?

No, if it was that one, I'd be tinkering with mysql+oltp. Everything
else I tested (limited time, but fairly wide spectrum) with that patch
was fine, including interactivity. Caveat: tbench/netperf test results
I'm not comfortable with, would need to backport to 26 to feel at all
confident with those. (fwtw)


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