Re: [PATCH] KVM: Don't use vcpu->requests for steal time accounting

Gleb Natapov
2012-12-14T15:41:19Z

On Sat, Dec 15, 2012 at 12:12:08AM +0900, Takuya Yoshikawa wrote:
> On Fri, 14 Dec 2012 13:28:15 +0200
> Gleb Natapov <gleb@redhat.com> wrote:
>
> > On Fri, Dec 14, 2012 at 07:37:18PM +0900, Takuya Yoshikawa wrote:
> > > We can check if accum_steal has any positive value instead of using
> > > KVM_REQ_STEAL_UPDATE bit in vcpu->requests; and this is the way we
> > > usually do for accounting for something in the kernel.
> > >
> > Now you added check that will be done on each guest entry, requests
> > mechanism prevents that.
>
> Yes, +1 "if" for the case we have nothing in requests.
>
Almost any bit in requests can be replaced by one "if". Those
if's add up.

> I'm not sure if setting and clearing a bit for that minor
> optimization is worth it.
>
Setting/clearing it should be much more rare than guest entry.

--
Gleb.