On Fri, Aug 12, 2022 at 9:24 AM Colton Lewis <coltonlewis@xxxxxxxxxx> wrote:
>
> On Wed, Aug 10, 2022 at 04:49:23PM -0700, David Matlack wrote:
> > On Wed, Aug 10, 2022 at 05:58:30PM +0000, Colton Lewis wrote:
> > > diff --git a/tools/testing/selftests/kvm/lib/perf_test_util.c b/tools/testing/selftests/kvm/lib/perf_test_util.c
> > > index 3c7b93349fef..9838d1ad9166 100644
> > > --- a/tools/testing/selftests/kvm/lib/perf_test_util.c
> > > +++ b/tools/testing/selftests/kvm/lib/perf_test_util.c
> > > @@ -52,6 +52,9 @@ void perf_test_guest_code(uint32_t vcpu_idx)
> > > struct perf_test_vcpu_args *vcpu_args = &pta->vcpu_args[vcpu_idx];
> > > uint64_t gva;
> > > uint64_t pages;
> > > + uint64_t addr;
> > > + bool random_access = pta->random_access;
> > > + bool populated = false;
> > > int i;
> > >
> > > gva = vcpu_args->gva;
> > > @@ -62,7 +65,11 @@ void perf_test_guest_code(uint32_t vcpu_idx)
> > >
> > > while (true) {
> > > for (i = 0; i < pages; i++) {
> > > - uint64_t addr = gva + (i * pta->guest_page_size);
> > > + if (populated && random_access)
> >
> > Skipping the populate phase makes sense to ensure everything is
> > populated I guess. What was your rational?
>
> That's it. Wanted to ensure everything was populated. Random
> population won't hit every page, but those unpopulated pages might be
> hit on subsequent iterations. I originally let population be random
> too and suspect this was driving an odd behavior I noticed early in
> testing where later iterations would be much faster than earlier ones.
>
> > Either way I think this policy should be driven by the test, rather than
> > harde-coded in perf_test_guest_code(). i.e. Move the call
> > perf_test_set_random_access() in dirty_log_perf_test.c to just after the
> > population phase.
>
> That makes sense. Will do.
Ah but if you get rid of the table refill between iterations, each
vCPU will access the same pages every iteration. At that point there's
no reason to distinguish the populate phase from the other phases, so
perhaps just drop the special case for the populate phase altogether?
