linux-kernel - [PATCH][mmotm] Sched fix stale value in average load per task

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Message-ID: <20081112104900.GA13896@balbir.in.ibm.com>
Date:	Wed, 12 Nov 2008 16:19:00 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Cc:	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Vaidyanathan S <svaidyan@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>
Subject: [PATCH][mmotm] Sched fix stale value in average load per task

cpu_avg_load_per_task() returns a stale value when nr_running is 0. It returns
an older stale (caculated when nr_running was non zero) value. This patch
returns and sets rq->avg_load_per_task to zero when nr_running is 0.

Compile and boot tested on a x86_64 box.

Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
---

 kernel/sched.c |    2 ++
 1 file changed, 2 insertions(+)

diff -puN kernel/sched.c~sched-fix-stale-load-avg kernel/sched.c
--- linux-2.6.28-rc4/kernel/sched.c~sched-fix-stale-load-avg	2008-11-12 15:55:38.000000000 +0530
+++ linux-2.6.28-rc4-balbir/kernel/sched.c	2008-11-12 15:56:09.000000000 +0530
@@ -1430,6 +1430,8 @@ static unsigned long cpu_avg_load_per_ta
 
 	if (rq->nr_running)
 		rq->avg_load_per_task = rq->load.weight / rq->nr_running;
+	else
+		rq->avg_load_per_task = 0;
 
 	return rq->avg_load_per_task;
 }
_

-- 
	Balbir
--
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