[PATCH] sched: fix tracepoint in scheduler.

[PATCH] sched: fix tracepoint in scheduler.

[Dongsheng Yang]

In function set_task_cpu(), if cpu == new_cpu,
there is no migration happen. But current trace point
will raise a migration trace event.

This patch change trace point to right place,
only when migration really happen, an event will
be threw out.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>
---
 kernel/sched/core.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9cae286..6708aff 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -998,9 +998,8 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu)
 #endif
 #endif
 
-	trace_sched_migrate_task(p, new_cpu);
-
 	if (task_cpu(p) != new_cpu) {
+		trace_sched_migrate_task(p, new_cpu);
 		if (p->sched_class->migrate_task_rq)
 			p->sched_class->migrate_task_rq(p, new_cpu);
 		p->se.nr_migrations++;
-- 
1.8.2.1

Re: [PATCH] sched: fix tracepoint in scheduler.

[Rik van Riel]

On 04/03/2014 08:12 AM, Dongsheng Yang wrote:
> In function set_task_cpu(), if cpu == new_cpu,
> there is no migration happen. But current trace point
> will raise a migration trace event.
> 
> This patch change trace point to right place,
> only when migration really happen, an event will
> be threw out.
> 
> Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>

I don't see any obvious place where set_task_cpu is called
with cpu == new_cpu, but there might be an un-obvious place,
because that if looks like it's there for a reason :)

Acked-by: Rik van Riel <riel@redhat.com>

-- 
All rights reversed

Re: [PATCH] sched: fix tracepoint in scheduler.

[Peter Zijlstra]

On Thu, Apr 03, 2014 at 08:12:48PM +0800, Dongsheng Yang wrote:
> In function set_task_cpu(), if cpu == new_cpu,
> there is no migration happen. But current trace point
> will raise a migration trace event.
> 
> This patch change trace point to right place,
> only when migration really happen, an event will
> be threw out.

Yeah its there so we can see pointless 'migrations'.

Re: [PATCH] sched: fix tracepoint in scheduler.

[Dongsheng Yang]

Hi Peter, did you forget to take this patch? :-)

On Fri, Apr 4, 2014 at 8:52 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, Apr 03, 2014 at 08:12:48PM +0800, Dongsheng Yang wrote:
>> In function set_task_cpu(), if cpu == new_cpu,
>> there is no migration happen. But current trace point
>> will raise a migration trace event.
>>
>> This patch change trace point to right place,
>> only when migration really happen, an event will
>> be threw out.
>
> Yeah its there so we can see pointless 'migrations'.
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Re: [PATCH] sched: fix tracepoint in scheduler.

[Peter Zijlstra]

On Wed, May 21, 2014 at 06:03:53PM +0800, Dongsheng Yang wrote:
> Hi Peter, did you forget to take this patch? :-)

No, I skipped it on purpose, its useful to be able to see if code tries
to do superfluous migrations.