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: Ilkka Koskinen <ilkka@os.amperecomputing.com>
Link: https://lore.kernel.org/r/20240906191539.4847-1-ilkka@os.amperecomputing.comSigned-off-by: Will Deacon <will@kernel.org>

drivers/perf/arm_pmuv3.c

@@ -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;
 	}