linux-kernel - [PATCH 2/3] sched: drop group_capacity to 1 only if remote group has no running tasks

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Message-Id: <1285633798-26886-3-git-send-email-ncrao@google.com>
Date:	Mon, 27 Sep 2010 17:29:57 -0700
From:	Nikhil Rao <ncrao@...gle.com>
To:	Ingo Molnar <mingo@...e.hu>, Peter Zijlstra <peterz@...radead.org>,
	Mike Galbraith <efault@....de>
Cc:	Venkatesh Pallipadi <venki@...gle.com>,
	linux-kernel@...r.kernel.org, Nikhil Rao <ncrao@...gle.com>
Subject: [PATCH 2/3] sched: drop group_capacity to 1 only if remote group has no running tasks

When SD_PREFER_SIBLING is set on a sched domain, drop group_capacity to 1
only if the remote sched group has no running tasks. This addresses the case
where you have two tasks on one socket and the other socket is idle, in which
case you drop the capacity to 1. If the remote group has >=1 running task, then
there is no difference from a cache-sharing perspective.

Signed-off-by: Nikhil Rao <ncrao@...gle.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 de8a6a0..33a7985 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -2548,7 +2548,7 @@ static inline void update_sd_lb_stats(struct sched_domain *sd, int this_cpu,
 		 * first, lower the sg capacity to one so that we'll try
 		 * and move all the excess tasks away.
 		 */
-		if (prefer_sibling)
+		if (prefer_sibling && !sgs.sum_nr_running)
 			sgs.group_capacity = min(sgs.group_capacity, 1UL);
 
 		if (local_group) {
-- 
1.7.1

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