From: Paul Turner <pjt@google.com>
Date: Wed, 6 Jul 2011 02:07:21 +0000 (-0700)
Subject: sched: update correct entity's runtime in check_preempt_wakeup()
X-Git-Tag: v3.1-rc1~298^2~9
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9bbd7374361d9bfc75108c3ad1c1b6db28b1be59;p=pandora-kernel.git

sched: update correct entity's runtime in check_preempt_wakeup()

While looking at check_preempt_wakeup() I realized that we are
potentially updating the wrong entity in the fair-group scheduling
case. In this case the current task's cfs_rq may not be the same as
the one used for the comparison between the waking task and the
existing task's vruntime.

This potentially results in us using a stale vruntime in the
pre-emption decision, providing a small false preference for the
previous task. The effects of this are bounded since we always
perform a hierarchal update on the tick.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/CAPM31R+2Ke2urUZKao5W92_LupdR4AYEv-EZWiJ3tG=tEes2cw@mail.gmail.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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