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SubjectRe: [PATCH RFC] reduce runqueue lock contention
On Thu, May 20, 2010 at 11:23:12PM +0200, Peter Zijlstra wrote:
> On Thu, 2010-05-20 at 23:09 +0200, Peter Zijlstra wrote:
>
> > int try_to_wake_up(struct task *p, unsigned int mask, wake_flags)
> > {
> > int state = atomic_read(&p->state);
> >
> > do {
> > if (!(state & mask))
> > return 0;
> >
> > state = atomic_cmpxchg(&p->state, state, TASK_WAKING);
> > } while (state != TASK_WAKING);
>
> cpu = select_task_rq()
>
> and then somehow see we get set_task_cpu() done without races :-)
>
> > /* do this pending queue + ipi thing */
> >
> > return 1;
> > }

I tried not to set the task waking, since I was worried about races with
us getting queued somewhere else. But, I don't have a good handle on
all of that so I kind of chickened out. That's why my code falls back
to the full ttwu in a few cases.

Do you think the above could be an addition to my patch or that it's
required for my patch to work well?

-chris



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