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Message-Id: <1252408577.10770.14.camel@marge.simson.net>
Date: Tue, 08 Sep 2009 13:16:17 +0200
From: Mike Galbraith <efault@....de>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Ingo Molnar <mingo@...e.hu>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: [patch] sched: ensure than a child can't start left of it's
parent's vruntime at fork() time
sched: ensure than a child can't start left of it's parent's vruntime at fork() time.
With START_DEBIT we make room for the new task, but with child_runs_first,
the debit lands on the parent when we swap vruntimes. There's nothing to
prevent the parent's vruntime having been right of min_vruntime at fork()
time, meaning that the child can gain vruntime, thus increasing scheduling
latency for waiters.
Signed-off-by: Mike Galbraith <efault@....de>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <new-submission>
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index cc97ea4..eb1269c 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -728,11 +728,11 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
vruntime -= thresh;
}
-
- /* ensure we never gain time by being placed backwards. */
- vruntime = max_vruntime(se->vruntime, vruntime);
}
+ /* ensure we never gain time by being placed backwards. */
+ vruntime = max_vruntime(se->vruntime, vruntime);
+
se->vruntime = vruntime;
}
@@ -1756,6 +1757,8 @@ static void task_new_fair(struct rq *rq, struct task_struct *p)
sched_info_queued(p);
update_curr(cfs_rq);
+ if (curr)
+ se->vruntime = curr->vruntime;
place_entity(cfs_rq, se, 1);
/* 'curr' will be NULL if the child belongs to a different group */
--
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