Messages in this thread |  | | | Subject | Re: [PATCH][RFC]: mutex: adaptive spin | | From | Peter Zijlstra <> | | Date | Wed, 07 Jan 2009 07:32:50 +0100 |
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On Wed, 2009-01-07 at 11:57 +0800, Lai Jiangshan wrote: > Peter Zijlstra wrote: > > +void mutex_spin_or_schedule(struct mutex_waiter *waiter, long state, unsigned long *flags) > > +{ > > + struct mutex *lock = waiter->lock; > > + struct task_struct *task = waiter->task; > > + struct task_struct *owner = lock->owner; > > + struct rq *rq; > > + > > + if (!owner) > > + goto do_schedule; > > + > > + rq = task_rq(owner); > > + > > + if (rq->curr != owner) { > > +do_schedule: > > + __set_task_state(task, state); > > + spin_unlock_mutex(&lock->wait_lock, *flags); > > + schedule(); > > + } else { > > + spin_unlock_mutex(&lock->wait_lock, *flags); > > + for (;;) { > > + /* Stop spinning when there's a pending signal. */ > > + if (signal_pending_state(state, task)) > > + break; > > + > > + /* Owner changed, bail to revalidate state */ > > + if (lock->owner != owner) > > + break; > > + > > + /* Owner stopped running, bail to revalidate state */ > > + if (rq->curr != owner) > > + break; > > + > > 2 questions from my immature thought: > > 1) Do we need keep gcc from optimizing when we access lock->owner > and rq->curr in the loop?
cpu_relax() is a compiler barrier iirc.
> 2) "if (rq->curr != owner)" need become smarter. > schedule() > { > select_next > rq->curr = next; > contex_swith > } > we also spin when owner is select_next-ing in schedule(). > but select_next is not fast enough.
I'm not sure what you're saying here..
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