Messages in this thread | | | Subject | Re: [PATCH] locking/osq: Drop the overload of osq lock | From | panxinhui <> | Date | Sun, 26 Jun 2016 13:21:04 +0800 |
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> 在 2016年6月26日,03:20,Peter Zijlstra <peterz@infradead.org> 写道: > > On Sun, Jun 26, 2016 at 01:27:56AM +0800, panxinhui wrote: >>>> 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. >>>> >>> >> do you mean that the spinner detect itself had yield out during the >> big spin loop? >> >> It is very possible to happen. BUT if spinner(on this vcpu) yield >> out, the next spinner would break the spin loop. AND if spinner >> detect itself yield out once, it’s very possible to get the osq lock >> soon as long as the ower vcpu is running. >> >> SO I think we need just check the owner vcpu’s yield_count. > > I had a quick look at KVM and it looks like it only has > kvm_cpu::preempted, which would suggest the interface boqun proposed. > > We'll have to look at many of the other virt platforms as well to see > what they can do. > > We could also provide _both_ interfaces and a platform can implement > whichever variant (or both) it can. > the kvm code on ppc has implemented yield_count. It let me feel a little relaxed. :)
looks like we could introduce the interface like below.
bool vcpu_is_preempted(int cpu) { return arch_vcpu_is_preempted(cpu); }
#ifdef arch_vcpu_has_yield_count bool vcpu_has_preemtped_once(int cpu, unsigned int yield_count) { return arch_get_vcpu_yield_count() != yield_count; }
#else bool vcpu_has_preemtped_once(int cpu, unsigned int yield_count) { /*just let called know it is preepmpted*/ return vcpu_is_preempted(cpu); } #endif
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