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Message-ID: <tip-71a29aa7b600595d0ef373ea605ac656876d1f2f@git.kernel.org>
Date: Mon, 7 Sep 2009 20:37:28 GMT
From: tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
a.p.zijlstra@...llo.nl, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/balancing] sched: Deal with low-load in wake_affine()
Commit-ID: 71a29aa7b600595d0ef373ea605ac656876d1f2f
Gitweb: http://git.kernel.org/tip/71a29aa7b600595d0ef373ea605ac656876d1f2f
Author: Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Mon, 7 Sep 2009 18:28:05 +0200
Committer: Ingo Molnar <mingo@...e.hu>
CommitDate: Mon, 7 Sep 2009 20:39:06 +0200
sched: Deal with low-load in wake_affine()
wake_affine() would always fail under low-load situations where
both prev and this were idle, because adding a single task will
always be a significant imbalance, even if there's nothing
around that could balance it.
Deal with this by allowing imbalance when there's nothing you
can do about it.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
kernel/sched_fair.c | 12 +++++++++++-
1 files changed, 11 insertions(+), 1 deletions(-)
diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index d7fda41..cc97ea4 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1262,7 +1262,17 @@ wake_affine(struct sched_domain *this_sd, struct rq *this_rq,
tg = task_group(p);
weight = p->se.load.weight;
- balanced = 100*(tl + effective_load(tg, this_cpu, weight, weight)) <=
+ /*
+ * In low-load situations, where prev_cpu is idle and this_cpu is idle
+ * due to the sync cause above having dropped tl to 0, we'll always have
+ * an imbalance, but there's really nothing you can do about that, so
+ * that's good too.
+ *
+ * Otherwise check if either cpus are near enough in load to allow this
+ * task to be woken on this_cpu.
+ */
+ balanced = !tl ||
+ 100*(tl + effective_load(tg, this_cpu, weight, weight)) <=
imbalance*(load + effective_load(tg, prev_cpu, 0, weight));
/*
--
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