sched: fastpath cycle recovery [LWN.net]

From:		Mike Galbraith <efault@gmx.de>
To:		Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject:		[patch 0/12] sched: fastpath cycle recovery
Date:		Thu, 11 Mar 2010 10:49:10 +0100
Message-ID:		<1268300950.6785.27.camel@marge.simson.net>
Cc:		Ingo Molnar <mingo@elte.hu>, LKML <linux-kernel@vger.kernel.org>
Archive-link:		Article, Thread

Hi Peter,

The following patchlets take a pinned pipe-test context switch frequency
in tip from 663KHZ to 694KHZ, and an unpinned instance from 450KHz to
540KHz.  With these applied to tip.today, I have zero 31-12->today
regressions, and even some modest progressions.

The biggest difference is made by the first patch.  We have a problem
with nohz when waking cross-cpu, which given select_idle_sibling(), we
do quite a bit.  In testing netperf TCP_RR, hitting nohz code on every
micro-idle was eating ~10% of throughput, making cross-cpu wakeup a
loser.  These patchlets combined turned netperf TCP_RR cross-cpu vs
affine from big loser into a winner.

All of these are trivial, mostly axe murder, but cycles add up.

	-Mike

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