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

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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.com
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Ilkka Koskinen 2024-09-06 12:15:39 -07:00 committed by Will Deacon
parent 91df34ef2d
commit 5967a19f1c
1 changed files with 4 additions and 4 deletions
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8
drivers/perf/arm_pmuv3.c
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@ -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;
}