Messages in this thread | | | Date | Mon, 27 Jun 2016 16:21:55 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 3/3] locking/osq: Drop the overload of osq_lock() |
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On Mon, Jun 27, 2016 at 01:41:30PM -0400, Pan Xinhui wrote: > @@ -118,8 +123,17 @@ bool osq_lock(struct optimistic_spin_queue *lock) > while (!READ_ONCE(node->locked)) { > /* > * If we need to reschedule bail... so we can block. > + * An over-committed guest with more vCPUs than pCPUs > + * might fall in this loop and cause a huge overload. > + * This is because vCPU A(prev) hold the osq lock and yield out > + * vCPU B(node) wait ->locked to be set, IOW, it wait utill > + * vCPU A run and unlock the osq lock. Such spin is meaningless > + * use vcpu_is_preempted to detech such case. IF arch does not > + * support vcpu preempted check, vcpu_is_preempted is a macro > + * defined by false.
Or you could mention lock holder preemption and everybody will know what you're talking about.
> */ > - if (need_resched()) > + if (need_resched() || > + vcpu_is_preempted(node_cpu(node->prev)))
Did you really need that linebreak?
> goto unqueue; > > cpu_relax_lowlatency(); > -- > 2.4.11 >
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