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SubjectRe: [patch 3/21] x86, bts: wait until traced task has been scheduled out

* Metzger, Markus T <markus.t.metzger@intel.com> wrote:

> >-----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.

No, that's wrong, wait_task_inactive() waits until the task
deschedules.

Ingo


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