Re: [PATCHv3 1/1] locking/qspinlock/x86: Avoid test-and-set when PV_DEDICATED is set

[Radim Krcmar]

2017-11-09 17:17+0100, Peter Zijlstra:
> On Thu, Nov 09, 2017 at 05:05:36PM +0100, Radim Krcmar wrote:
> > 2017-11-09 10:53-0500, Pankaj Gupta:
> > > 2] PV TLB should also behave as per option PV_DEDICATED for better performance.
> > 
> > Right,
> 
> Shouldn't KVM do flush_tlb_other() in any case? Not sure how
> PV_DEDICATED can help with that.

It will, the suggestion was based on recent extension of the
flush_tlb_others implementaion, https://lkml.org/lkml/2017/11/8/1146.

PV_TLB_FLUSH allows a guest to set a flush bit instead of sending flush
IPI if the target VCPU is not running.  This would be a waste of time
with PV_DEDICATED as all VCPUs are expected to always running.

With PV_DEDICATED, the guest should keep using native_flush_tlb_others.