Re: [PATCH 3/3] locking/osq: Drop the overload of osq_lock()
From: Peter Zijlstra <peterz@infradead.org>
Date: 2016-06-27 14:22:09
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On Mon, Jun 27, 2016 at 01:41:30PM -0400, Pan Xinhui wrote:
quoted hunk ↗ jump to hunk
@@ -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