Subject: Re: [PATCH 0/4] pending scheduler updates
From: Mike Galbraith <efault@gmx.de>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>, Srivatsa Vaddagiri <vatsa@in.ibm.com>,
       LKML <linux-kernel@vger.kernel.org>
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Date: Wed, 22 Oct 2008 19:56:55 +0200
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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)

	-Mike

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