Re: [kvm-unit-tests Patch 2/5] x86: pmu: Change the minimum value of llc_misses event to 0

Jim Mattson
2023-10-24T13:06:33Z

On Tue, Oct 24, 2023 at 12:51 AM Dapeng Mi <dapeng1.mi@linux.intel.com> wrote:
>
> Along with the CPU HW's upgrade and optimization, the count of LLC
> misses event for running loop() helper could be 0 just like seen on
> Sapphire Rapids.
>
> So modify the lower limit of possible count range for LLC misses
> events to 0 to avoid LLC misses event test failure on Sapphire Rapids.

I'm not convinced that these tests are really indicative of whether or
not the PMU is working properly. If 0 is allowed for llc misses, for
instance, doesn't this sub-test pass even when the PMU is disabled?

Surely, we can do better.

> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> ---
> x86/pmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/x86/pmu.c b/x86/pmu.c
> index 0def28695c70..7443fdab5c8a 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -35,7 +35,7 @@ struct pmu_event {
> {"instructions", 0x00c0, 10*N, 10.2*N},
> {"ref cycles", 0x013c, 1*N, 30*N},
> {"llc references", 0x4f2e, 1, 2*N},
> - {"llc misses", 0x412e, 1, 1*N},
> + {"llc misses", 0x412e, 0, 1*N},
> {"branches", 0x00c4, 1*N, 1.1*N},
> {"branch misses", 0x00c5, 0, 0.1*N},
> }, amd_gp_events[] = {
> --
> 2.34.1
>