Re: [PATCH v2 1/4] arm_pmu: Add PERF_PMU_CAP_EXTENDED_HW_TYPE capability

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 7/24/23 19:14, James Clark 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@google.com>
> Acked-by: Ian Rogers <irogers@google.com>
> Signed-off-by: James Clark <james.clark@arm.com>

Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

> ---
>  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 f6ccb2cd4dfc..2e79201daa4a 100644
> --- a/drivers/perf/arm_pmu.c
> +++ b/drivers/perf/arm_pmu.c
> @@ -880,8 +880,13 @@ 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
> +		 * 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] =