From: Mike Galbraith <efault@gmx.de>
To: lkml <linux-kernel@vger.kernel.org>
Cc: Ingo Molnar <mingo@elte.hu>
Subject: [2.6.16-rc6 patch] smp fix for recalc_task_prio()
Date: Sat, 18 Mar 2006 05:37:17 +0100 [thread overview]
Message-ID: <1142656637.8262.9.camel@homer> (raw)
Greetings,
The patchlet below fixes an smp buglet where a task goes to sleep on one
cpu and wakes up on another, causing recalc_task_prio() to be called
with now < p->timestamp.
If this isn't 2.6.16 material, and I can respin against mm.
-Mike
--- linux-2.6.16-rc6/kernel/sched.c.org 2006-03-17 14:48:35.000000000 +0100
+++ linux-2.6.16-rc6/kernel/sched.c 2006-03-18 05:22:21.000000000 +0100
@@ -685,6 +685,16 @@
unsigned long long __sleep_time = now - p->timestamp;
unsigned long sleep_time;
+ /*
+ * On SMP systems, a task can go to sleep on one CPU and
+ * wake up on another. When this happens, the timestamp
+ * is rounded to the nearest tick, which can lead to now
+ * being less than p->timestamp for short sleeps. Ignore
+ * these, they're insignificant.
+ */
+ if (unlikely(now < p->timestamp))
+ __sleep_time = 0ULL;
+
if (unlikely(p->policy == SCHED_BATCH))
sleep_time = 0;
else {
next reply other threads:[~2006-03-18 4:35 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-03-18 4:37 Mike Galbraith [this message]
2006-03-18 4:41 ` [2.6.16-rc6 patch] smp fix for recalc_task_prio() Mike Galbraith
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