Messages in this thread |  | | | Date | Fri, 17 Dec 2010 20:28:14 +0100 | | From | Oleg Nesterov <> | | Subject | Re: [RFC][PATCH 5/5] sched: Reduce ttwu rq->lock contention |
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On 12/17, Peter Zijlstra wrote: > > By fully serializing all wakeups using ->pi_lock it becomes a lot > simpler
Hmm, yes. Contrary to my expectations ;)
> static int > try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > { > unsigned long flags; > int cpu, ret = 0; > > smp_wmb(); > raw_spin_lock_irqsave(&p->pi_lock, flags); > > if (!(p->state & state)) > goto unlock; > > ret = 1; /* we qualify as a proper wakeup now */ > > if (p->se.on_rq && ttwu_force(p, state, wake_flags)) > goto unlock;
Well. All I can say, I'll try to re-read this code with the fresh head ;) We should ensure that on_rq == 0 can not be racy.
> p->state = TASK_WAKING; > smp_wmb(); > raw_spin_unlock_wait(&task_rq(p)->lock);
This needs smp_mb(), unlock_wait() reads the memory.
Oleg.
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