linux-kernel - [PATCH] perf: arm_pmuv3: Use BR_RETIRED for HW branch event if enabled

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Message-ID: <20240905204732.20546-1-ilkka@os.amperecomputing.com>
Date: Thu,  5 Sep 2024 13:47:32 -0700
From: Ilkka Koskinen <ilkka@...amperecomputing.com>
To: Will Deacon <will@...nel.org>,
	Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	ilkka@...amperecomputing.com
Subject: [PATCH] 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.

Signed-off-by: Ilkka Koskinen <ilkka@...amperecomputing.com>
---
 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;
-
-		return HW_OP_UNSUPPORTED;
-	}
-
-	return armpmu_map_event(event, &armv8_pmuv3_perf_map,
-				&armv8_pmuv3_perf_cache_map,
-				ARMV8_PMU_EVTYPE_EVENT);
-}
-
 static int __armv8_pmuv3_map_event(struct perf_event *event,
 				   const unsigned (*extra_event_map)
 						  [PERF_COUNT_HW_MAX],
@@ -1116,7 +1095,9 @@ static int __armv8_pmuv3_map_event(struct perf_event *event,
 	int hw_event_id;
 	struct arm_pmu *armpmu = to_arm_pmu(event->pmu);
 
-	hw_event_id = __armv8_pmuv3_map_event_id(armpmu, event);
+	hw_event_id = armpmu_map_event(event, &armv8_pmuv3_perf_map,
+				       &armv8_pmuv3_perf_cache_map,
+				       ARMV8_PMU_EVTYPE_EVENT);
 
 	/*
 	 * CHAIN events only work when paired with an adjacent counter, and it
-- 
2.42.0