Commit 5967a19f authored by Ilkka Koskinen's avatar Ilkka Koskinen Committed by Will Deacon
Browse files

perf: arm_pmuv3: Use BR_RETIRED for HW branch event if enabled 



The PMU driver attempts to use PC_WRITE_RETIRED for the HW branch event,
if enabled. However, PC_WRITE_RETIRED counts only taken branches,
whereas BR_RETIRED counts also non-taken ones.

Furthermore, perf uses HW branch event to calculate branch misses ratio,
implying BR_RETIRED is the correct event to count.

We keep PC_WRITE_RETIRED still as an option in case BR_RETIRED isn't
implemented.

Signed-off-by: default avatarIlkka Koskinen <ilkka@os.amperecomputing.com>
Link: https://lore.kernel.org/r/20240906191539.4847-1-ilkka@os.amperecomputing.com


Signed-off-by: default avatarWill Deacon <will@kernel.org>
parent 91df34ef

drivers/perf/arm_pmuv3.c

+4 −4
Original line number Diff line number Diff line
@@ -1086,14 +1086,14 @@ static int __armv8_pmuv3_map_event_id(struct arm_pmu *armpmu, 
	if (event->attr.type == PERF_TYPE_HARDWARE &&

	    event->attr.config == PERF_COUNT_HW_BRANCH_INSTRUCTIONS) {



		if (test_bit(ARMV8_PMUV3_PERFCTR_PC_WRITE_RETIRED,

			     armpmu->pmceid_bitmap))

			return ARMV8_PMUV3_PERFCTR_PC_WRITE_RETIRED;



		if (test_bit(ARMV8_PMUV3_PERFCTR_BR_RETIRED,

			     armpmu->pmceid_bitmap))

			return ARMV8_PMUV3_PERFCTR_BR_RETIRED;



		if (test_bit(ARMV8_PMUV3_PERFCTR_PC_WRITE_RETIRED,

			     armpmu->pmceid_bitmap))

			return ARMV8_PMUV3_PERFCTR_PC_WRITE_RETIRED;



		return HW_OP_UNSUPPORTED;

	}