Re: [RFC PATCH 3/3] KVM: selftests: Add vgic initialization for dirty log perf test for ARM

[Jing Zhang <jingzhangos@google.com>]

On Tue, Jan 11, 2022 at 2:30 AM Marc Zyngier <maz@kernel.org> wrote:
>
> On Mon, 10 Jan 2022 21:04:41 +0000,
> Jing Zhang <jingzhangos@google.com> wrote:
> >
> > For ARM64, if no vgic is setup before the dirty log perf test, the
> > userspace irqchip would be used, which would affect the dirty log perf
> > test result.
>
> Doesn't it affect *all* performance tests? How much does this change
> contributes to the performance numbers you give in the cover letter?
>
This bottleneck showed up after adding the fast path patch. I didn't
try other performance tests with this, but I think it is a good idea
to add a vgic setup for all performance tests. I can post another
patch later to make it available for all performance tests after
finishing this one and verifying all other performance tests.
Below is the test result without adding the vgic setup. It shows
20~30% improvement for the different number of vCPUs.
+-------+------------------------+
    | #vCPU | dirty memory time (ms) |
    +-------+------------------------+
    | 1     | 965                    |
    +-------+------------------------+
    | 2     | 1006                    |
    +-------+------------------------+
    | 4     | 1128                    |
    +-------+------------------------+
    | 8     | 2005                   |
    +-------+------------------------+
    | 16    | 3903                   |
    +-------+------------------------+
    | 32    | 7595                   |
    +-------+------------------------+
    | 64    | 15783                  |
    +-------+------------------------+
> >
> > Signed-off-by: Jing Zhang <jingzhangos@google.com>
> > ---
> >  tools/testing/selftests/kvm/dirty_log_perf_test.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> >
> > diff --git a/tools/testing/selftests/kvm/dirty_log_perf_test.c b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> > index 1954b964d1cf..b501338d9430 100644
> > --- a/tools/testing/selftests/kvm/dirty_log_perf_test.c
> > +++ b/tools/testing/selftests/kvm/dirty_log_perf_test.c
> > @@ -18,6 +18,12 @@
> >  #include "test_util.h"
> >  #include "perf_test_util.h"
> >  #include "guest_modes.h"
> > +#ifdef __aarch64__
> > +#include "aarch64/vgic.h"
> > +
> > +#define GICD_BASE_GPA                        0x8000000ULL
> > +#define GICR_BASE_GPA                        0x80A0000ULL
>
> How did you pick these values?
I used the same values from other tests.
Talked with Raghavendra about the values. It could be arbitrary and he
chose these values from QEMU's configuration.
>
> Thanks,
>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.
Thanks,
Jing