> 在 2016年6月26日，03:20，Peter Zijlstra <pet...@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
