Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler

[Raghavendra K T]

On 07/11/2012 05:25 PM, Christian Borntraeger wrote:
> On 11/07/12 13:51, Raghavendra K T wrote:
> > > > > Almost all s390 kernels use diag9c (directed yield to a given guest cpu) for spinlocks, though.
> > > >
> > > > Perhaps x86 should copy this.
> > >
> > > See arch/s390/lib/spinlock.c
> > > The basic idea is using several heuristics:
> > > - loop for a given amount of loops
> > > - check if the lock holder is currently scheduled by the hypervisor
> > >     (smp_vcpu_scheduled, which uses the sigp sense running instruction)
> > >     Dont know if such thing is available for x86. It must be a lot cheaper
> > >     than a guest exit to be useful
> >
> > Unfortunately we do not have information on lock-holder.
>
> That would be an independent patch and requires guest changes.

Yes, AFAI think, there are two options:
(1) extend lock and use spare bit in ticketlock indicate lock is held
(2) use percpu list entry.



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