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SubjectRE: [patch 3/21] x86, bts: wait until traced task has been scheduled out
>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@elte.hu]
>Sent: Wednesday, April 01, 2009 1:42 PM
>To: Oleg Nesterov; Peter Zijlstra


>* Oleg Nesterov <oleg@redhat.com> wrote:
>
>> On 03/31, Markus Metzger wrote:
>> >
>> > +static void wait_to_unschedule(struct task_struct *task)
>> > +{
>> > + unsigned long nvcsw;
>> > + unsigned long nivcsw;
>> > +
>> > + if (!task)
>> > + return;
>> > +
>> > + if (task == current)
>> > + return;
>> > +
>> > + nvcsw = task->nvcsw;
>> > + nivcsw = task->nivcsw;
>> > + for (;;) {
>> > + if (!task_is_running(task))
>> > + break;
>> > + /*
>> > + * The switch count is incremented before the actual
>> > + * context switch. We thus wait for two switches to be
>> > + * sure at least one completed.
>> > + */
>> > + if ((task->nvcsw - nvcsw) > 1)
>> > + break;
>> > + if ((task->nivcsw - nivcsw) > 1)
>> > + break;
>> > +
>> > + schedule();
>>
>> schedule() is a nop here. We can wait unpredictably long...
>>
>> Ingo, do have have any ideas to improve this helper?
>
>hm, there's a similar looking existing facility:
>wait_task_inactive(). Have i missed some subtle detail that makes it
>inappropriate for use here?


wait_task_inactive() waits until the task is no longer TASK_RUNNING.

I need to wait until the task has been scheduled out at least once.


regards,
markus.

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