On 9/6/24 02:17, Ilkka Koskinen wrote:
The PMU driver attempts to use PC_WRITE_RETIRED for the HW branch event,But is the event BR_RETIRED always guaranteed to be available. Should not
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.
armpmu->pmceid_bitmap be checked first ?
Signed-off-by: Ilkka Koskinen <ilkka@xxxxxxxxxxxxxxxxxxxxxx>
---
drivers/perf/arm_pmuv3.c | 27 ++++-----------------------
1 file changed, 4 insertions(+), 23 deletions(-)
diff --git a/drivers/perf/arm_pmuv3.c b/drivers/perf/arm_pmuv3.c
index d246840797b6..a8ed08df1411 100644
--- a/drivers/perf/arm_pmuv3.c
+++ b/drivers/perf/arm_pmuv3.c
@@ -46,6 +46,7 @@ static const unsigned armv8_pmuv3_perf_map[PERF_COUNT_HW_MAX] = {
[PERF_COUNT_HW_INSTRUCTIONS] = ARMV8_PMUV3_PERFCTR_INST_RETIRED,
[PERF_COUNT_HW_CACHE_REFERENCES] = ARMV8_PMUV3_PERFCTR_L1D_CACHE,
[PERF_COUNT_HW_CACHE_MISSES] = ARMV8_PMUV3_PERFCTR_L1D_CACHE_REFILL,
+ [PERF_COUNT_HW_BRANCH_INSTRUCTIONS] = ARMV8_PMUV3_PERFCTR_BR_RETIRED,
[PERF_COUNT_HW_BRANCH_MISSES] = ARMV8_PMUV3_PERFCTR_BR_MIS_PRED,
[PERF_COUNT_HW_BUS_CYCLES] = ARMV8_PMUV3_PERFCTR_BUS_CYCLES,
[PERF_COUNT_HW_STALLED_CYCLES_FRONTEND] = ARMV8_PMUV3_PERFCTR_STALL_FRONTEND,
@@ -1083,28 +1084,6 @@ static void armv8pmu_reset(void *info)
armv8pmu_pmcr_write(pmcr);
}
-static int __armv8_pmuv3_map_event_id(struct arm_pmu *armpmu,
- struct perf_event *event)
-{
- 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 BR_RETIRED event is absent on the platform, PC_WRITE_RETIRED still remains
a good alternative to fallback on. Hence wondering if the above order could
just be changed to use BR_RETIRED first when available.