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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>
This commit is contained in:
Paul Turner 2011-07-05 19:07:21 -07:00 committed by Ingo Molnar
parent 994bf1c922
commit 9bbd737436
1 changed files with 1 additions and 1 deletions
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2
kernel/sched_fair.c
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@ -1919,8 +1919,8 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
if (!sched_feat(WAKEUP_PREEMPT))
return;
update_curr(cfs_rq);
find_matching_se(&se, &pse);
update_curr(cfs_rq_of(se));
BUG_ON(!pse);
if (wakeup_preempt_entity(se, pse) == 1) {
/*