linux-kernel - [RFC -v6 PATCH 1/8] sched: check the right ->nr_running in yield_task

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Message-ID: <20110120163236.60ce3079@annuminas.surriel.com>
Date:	Thu, 20 Jan 2011 16:32:36 -0500
From:	Rik van Riel <riel@...hat.com>
To:	kvm@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Avi Kiviti <avi@...hat.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>,
	Chris Wright <chrisw@...s-sol.org>, ttracy@...hat.com,
	dshaks@...hat.com, "Nakajima, Jun" <jun.nakajima@...el.com>
Subject: [RFC -v6 PATCH 1/8] sched: check the right ->nr_running in
 yield_task_fair

With CONFIG_FAIR_GROUP_SCHED, each task_group has its own cfs_rq.
Yielding to a task from another cfs_rq may be worthwhile, since
a process calling yield typically cannot use the CPU right now.

Therefor, we want to check the per-cpu nr_running, not the
cgroup local one.

Signed-off-by: Rik van Riel <riel@...hat.com>
---
 kernel/sched_fair.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index c62ebae..7b338ac 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1304,7 +1304,7 @@ static void yield_task_fair(struct rq *rq)
 	/*
 	 * Are we the only task in the tree?
 	 */
-	if (unlikely(cfs_rq->nr_running == 1))
+	if (unlikely(rq->nr_running == 1))
 		return;
 
 	clear_buddies(cfs_rq, se);

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