Re: [PATCH] locking/osq: Drop the overload of osq lock

[Peter Zijlstra]

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, itâs 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 vcpuâs 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.