linux-kernel - Re: [PATCH 0/4] pending scheduler updates

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Message-Id: <1224671528.7511.11.camel@marge.simson.net>
Date:	Wed, 22 Oct 2008 12:32:08 +0200
From:	Mike Galbraith <efault@....de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/4] pending scheduler updates

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.

	-Mike 

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