[PATCH 1/4] arm_pmu: Add PERF_PMU_CAP_EXTENDED_HW_TYPE capability

[James Clark]

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 at google.com>
Signed-off-by: James Clark <james.clark at 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 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