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

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Message-ID: <CANgfPd-7Yb05BYBW7TOg67qq=_vSXqrRQ_XF7WUfstQjXgyPww@mail.gmail.com>
Date:   Thu, 26 Jan 2023 14:51:58 -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 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.

>
>
> > +       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.