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SubjectRe: [patch 05/15] Generic Mutex Subsystem, mutex-core.patch

* Oleg Nesterov <oleg@tv-sign.ru> wrote:

> > +__mutex_wakeup_waiter(struct mutex *lock __IP_DECL__)
> > +{
> > + struct mutex_waiter *waiter;
> > ...
> > + if (!waiter->woken) {
> > + waiter->woken = 1;
> > + wake_up_process(waiter->ti->task);
> > + }
>
> Is it optimization? If yes - why? From mutex.h:
>
> - only one task can hold the mutex at a time
> - only the owner can unlock the mutex
>
> So, how can this help?

yes, it's an optimization. I've removed it from the latest queue because
it didnt trigger all that often, but the optimization is valid: while we
have a 'waiter in flight', another (fast) task might grab the mutex, and
might release it - in which case it could attempt to wake up the waiter
again - which this flag optimizes.

Ingo
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