Messages in this thread | | | Date | Sat, 25 Jun 2016 18:15:40 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] locking/osq: Drop the overload of osq lock |
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On Sat, Jun 25, 2016 at 11:21:30PM +0800, Boqun Feng wrote: > So on PPC, we have lppaca::yield_count to detect when an vcpu is > preempted, if the yield_count is even, the vcpu is running, otherwise it > is preempted(__spin_yield() is a user of this). > > Therefore it makes more sense we > > if (need_resched() || vcpu_is_preempted(old)) > > here, and implement vcpu_is_preempted() on PPC as > > bool vcpu_is_preempted(int cpu) > { > return !!(be32_to_cpu(lppaca_of(cpu).yield_count) & 1) > } > > Thoughts?
Would that not have issues where the owner cpu is kept running but the spinner (ie. _this_ vcpu) gets preempted? I would think that in that case we too want to stop spinning.
Although, if all vcpus are scheduled equal, it might not matter on average.
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