linux-kernel - Re: [PATCH v4 2/2] selftests: KVM: Add dirty logging page splitting test

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Date:   Thu, 26 Jan 2023 15:11:52 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     Vipin Sharma <vipinsh@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Ricardo Koller <ricarkol@...gle.com>
Subject: Re: [PATCH v4 2/2] selftests: KVM: Add dirty logging page splitting test

On Thu, Jan 26, 2023 at 3:04 PM Vipin Sharma <vipinsh@...gle.com> wrote:
>
> On Thu, Jan 26, 2023 at 2:52 PM Ben Gardon <bgardon@...gle.com> wrote:
> >
> > On Thu, Jan 26, 2023 at 12:06 PM Vipin Sharma <vipinsh@...gle.com> wrote:
> > >
> > > On Wed, Jan 25, 2023 at 10:23 AM Ben Gardon <bgardon@...gle.com> wrote:
> > >
> > > > +static void run_vcpus_get_page_stats(struct kvm_vm *vm, struct kvm_page_stats *stats, const char *stage)
> > > > +{
> > > > +       int i;
> > > > +
> > > > +       iteration++;
> > > > +       for (i = 0; i < VCPUS; i++) {
> > > > +               while (READ_ONCE(vcpu_last_completed_iteration[i]) !=
> > > > +                      iteration)
> > > > +                       ;
> > > > +       }
> > > > +
> > > > +       get_page_stats(vm, stats, stage);
> > >
> > > get_page_stats() is already called in run_test() explicitly for other
> > > stats. I think it's better to split this function and make the flow
> > > like:
> > >
> > > run_vcpus_till_iteration(iteration++);
> > > get_page_stats(vm, &stats_populated, "populating memory");
> > >
> > > This makes it easy to follow run_test_till_iteration() and easy to see
> > > where stats are collected. run_test_till_iteration() can also be a
> > > library function used by other tests like dirty_log_perf_test
> >
> > Yeah, either way works. We can do it all in the run_tests function as
> > I originally had or we can have the run vcpus and get stats in a
> > helper as David suggested or we can separate run_vcpus and get_stats
> > helpers as you're suggesting. I don't think it makes much of a
> > difference.
> > If you feel strongly I can send out another iteration of this test.
> >
>
> I should have read David's comment and responded in that version.
> No strong feelings. It is up to you.

No worries, it probably would have been easier to track down if I had
links in the cover letter. :)

>
> > >
> > >
> > > > +       dirty_log_manual_caps = 0;
> > > > +       for_each_guest_mode(run_test, NULL);
> > > > +
> > > > +       dirty_log_manual_caps =
> > > > +               kvm_check_cap(KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2);
> > > > +
> > > > +       if (dirty_log_manual_caps) {
> > > > +               dirty_log_manual_caps &= (KVM_DIRTY_LOG_MANUAL_PROTECT_ENABLE |
> > > > +                                         KVM_DIRTY_LOG_INITIALLY_SET);
> > > > +               for_each_guest_mode(run_test, NULL);
> > > > +       }
> > >
> > > Should there be a message to show  that this capability is not tested
> > > as it is not available?
> > > Or, there can be a command line option to explicitly provide intent of
> > > testing combined,  split modes, or both? Then test can error out
> > > accordingly.
> >
> > Sure, that would work too. If I send another version of this series I
> > can add a skip message, but I don't want to re-add an option to
> > specify whether to run with MANUAL_PROTECT, because that's what I had
> > originally and then David suggested I remove it and just always run
> > both.
>
> Sounds good.
>
> Reviewed-By: Vipin Sharma <vipinsh@...gle.com>

Thanks!