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

[Peter Zijlstra]

On Sun, Jun 26, 2016 at 12:28:13AM +0800, Boqun Feng wrote:
> On Sat, Jun 25, 2016 at 06:09:22PM +0200, Peter Zijlstra wrote:
> > That works here, but it would not work for the need_resched() in
> > mutex_spin_on_owner() and mutex_optimistic_spin() which need equal
> > treatment.
> > 
> > Because those too we want to limit.
> > 
> > The count thing, while a little more cumbersome, is more widely
> > applicable than just the one OSQ case where we happen to have a cpu
> > number.
> > 
> 
> But if we don't have a cpu number, which vcpu's preemption are we
> trying to detect? 

_this_ vcpu's preemption. If the yield count of this cpu changes, we
know this vcpu has been scheduled and we should stop spinning.

This is similar to the need_resched() case, which check is _this_ cpu
should reschedule.