linux-kernel - [PATCH] sched: Revert 738d2be, Simplify set_task

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Message-ID: <1261492999.4937.36.camel@laptop>
Date:	Tue, 22 Dec 2009 15:43:19 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, efault@....de
Subject: [PATCH] sched: Revert 738d2be, Simplify set_task_cpu()

[ and now with Subject ]

Effectively reverts 738d2be4301007f054541c5c4bf7fb6a361c9b3a.

As demonstrated by Eric, we really need to call __set_task_cpu() early
in the fork() path to properly initialize the various task state --
specifically the cgroup state through set_task_rq().

[ we could probably fix this by explicitly calling __set_task_cpu() from
  sched_fork(), but lets try that for the next cycle and simply revert
  to the old behaviour for now. ]

Reported-by: Eric Paris <eparis@...hat.com>
Tested-by: Eric Paris <eparis@...hat.com>, 
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 kernel/sched.c |    9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

Index: linux-2.6/kernel/sched.c
===================================================================
--- linux-2.6.orig/kernel/sched.c
+++ linux-2.6/kernel/sched.c
@@ -2067,11 +2067,10 @@ void set_task_cpu(struct task_struct *p,
 
 	trace_sched_migrate_task(p, new_cpu);
 
-	if (task_cpu(p) == new_cpu)
-		return;
-
-	p->se.nr_migrations++;
-	perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, 1, NULL, 0);
+	if (task_cpu(p) != new_cpu) {
+		p->se.nr_migrations++;
+		perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, 1, NULL, 0);
+	}
 
 	__set_task_cpu(p, new_cpu);
 }



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