linux-kernel - [PATCH] sched: avoid overpull when pulling RT task

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Date:	Sun, 15 May 2011 12:35:02 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>,
	Yong Zhang <yong.zhang0@...il.com>
Subject: [PATCH] sched: avoid overpull when pulling RT task

When pulling RT task for a given runqueue, pulling is continued even
after certain RT tasks get pulled, in case there are still higher
priority tasks on other runqueues, though it is low likelihood as the
comment says. The load of of this runqueue, on other hand, should also
be concerned. If it is overloaded, the low likelihood should be
abandoned to avoid overpull.

Signed-off-by: Hillf Danton <dhillf@...il.com>
---
 kernel/sched_rt.c |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 14c764b..b425ca1 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1508,6 +1508,11 @@ static int pull_rt_task(struct rq *this_rq)
 		}
 skip:
 		double_unlock_balance(this_rq, src_rq);
+
+		/* if pulled we have to also avoid overpull */
+		if (ret == 1)
+			if (likely(rt_overloaded(this_rq)))
+				break;
 	}

 	return ret;
--
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