From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Tue, 31 Jul 2012 00:19:25 +0000 (-0700)
Subject: rcu: Reduce synchronize_rcu_expedited() latency
X-Git-Tag: omap-for-v3.7-rc1/fixes-cpufreq-signed~101^2~1^2~6
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1943c89de700248d68385300a9b5588a1e314f90;p=pandora-kernel.git

rcu: Reduce synchronize_rcu_expedited() latency

The synchronize_rcu_expedited() function disables interrupts across a
scan of all leaf rcu_node structures, which is not good for real-time
scheduling latency on large systems (hundreds or especially thousands
of CPUs).  This commit therefore holds off CPU-hotplug operations using
get_online_cpus(), and removes the prior acquisiion of the ->onofflock
(which required disabling interrupts).

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
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