Re: [PATCH 1/4] arm_pmu: Add PERF_PMU_CAP_EXTENDED_HW_TYPE capability

[Ian Rogers]

On Mon, Jul 10, 2023 at 5:22 AM James Clark <james.clark@xxxxxxx> wrote:
>
> This capability gives us the ability to open PERF_TYPE_HARDWARE and
> PERF_TYPE_HW_CACHE events on a specific PMU for free. All the
> implementation is contained in the Perf core and tool code so no change
> to the Arm PMU driver is needed.
>
> The following basic use case now results in Perf opening the event on
> all PMUs rather than picking only one in an unpredictable way:
>
>   $ perf stat -e cycles -- taskset --cpu-list 0,1 stress -c 2
>
>    Performance counter stats for 'taskset --cpu-list 0,1 stress -c 2':
>
>          963279620      armv8_cortex_a57/cycles/                (99.19%)
>          752745657      armv8_cortex_a53/cycles/                (94.80%)
>
> Fixes: 55bcf6ef314a ("perf: Extend PERF_TYPE_HARDWARE and PERF_TYPE_HW_CACHE")
> Suggested-by: Ian Rogers <irogers@xxxxxxxxxx>
> Signed-off-by: James Clark <james.clark@xxxxxxx>

Acked-by: Ian Rogers <irogers@xxxxxxxxxx>

Thanks,
Ian

> ---
>  drivers/perf/arm_pmu.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
> index 277e29fbd504..d8844a9461a2 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -875,8 +875,13 @@ struct arm_pmu *armpmu_alloc(void)
>                  * configuration (e.g. big.LITTLE). This is not an uncore PMU,
>                  * and we have taken ctx sharing into account (e.g. with our
>                  * pmu::filter callback and pmu::event_init group validation).
> +                *
> +                * PERF_PMU_CAP_EXTENDED_HW_TYPE is required to open the legacy
> +                * PERF_TYPE_HARDWARE and PERF_TYPE_HW_CACHE events on a
> +                * specific PMU.
>                  */
> -               .capabilities   = PERF_PMU_CAP_HETEROGENEOUS_CPUS | PERF_PMU_CAP_EXTENDED_REGS,
> +               .capabilities   = PERF_PMU_CAP_HETEROGENEOUS_CPUS | PERF_PMU_CAP_EXTENDED_REGS |
> +                                 PERF_PMU_CAP_EXTENDED_HW_TYPE,
>         };
>
>         pmu->attr_groups[ARMPMU_ATTR_GROUP_COMMON] =
> --
> 2.34.1
>