[PATCH v4] arm64: pmuv3: dynamically map PERF_COUNT_HW_BRANCH_INSTRUCTIONS

[Peter Newman]

From: Stephane Eranian <eranian at google.com>

The mapping of perf_events generic hardware events to actual PMU events on
ARM PMUv3 may not always be correct. This is in particular true for the
PERF_COUNT_HW_BRANCH_INSTRUCTIONS event. Although the mapping points to an
architected event, it may not always be available. This can be seen with a
simple:

$ perf stat -e branches sleep 0
 Performance counter stats for 'sleep 0':

   <not supported>      branches

       0.001401081 seconds time elapsed

Yet the hardware does have an event that could be used for branches.

Dynamically check for a supported hardware event which can be used for
PERF_COUNT_HW_BRANCH_INSTRUCTIONS at mapping time.

And with that:

$ perf stat -e branches sleep 0

 Performance counter stats for 'sleep 0':

           166,739      branches

       0.000832163 seconds time elapsed

Based-on: https://lore.kernel.org/all/YvunKCJHSXKz%2FkZB@FVFF77S0Q05N
Based-on-patch-by: Mark Rutland <mark.rutland at arm.com>
Signed-off-by: Stephane Eranian <eranian at google.com>
Signed-off-by: Peter Newman <peternewman at google.com>
---
v3->v4:
 - splice Mark's patch with Stephane's problem statement
v2->v3:
 - removed prints per Will's suggestion
 
[v3] https://lore.kernel.org/all/20220816130221.885920-1-peternewman@google.com/
[v2] https://lore.kernel.org/lkml/20220324181458.3216262-1-eranian@google.com/

 arch/arm64/kernel/perf_event.c | 27 +++++++++++++++++++++++----
 1 file changed, 23 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c
index dde06c0f97f3..ee63f8e719ea 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -45,7 +45,6 @@ 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_PC_WRITE_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,
@@ -1048,6 +1047,28 @@ 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],
@@ -1059,9 +1080,7 @@ 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 = armpmu_map_event(event, &armv8_pmuv3_perf_map,
-				       &armv8_pmuv3_perf_cache_map,
-				       ARMV8_PMU_EVTYPE_EVENT);
+	hw_event_id = __armv8_pmuv3_map_event_id(armpmu, event);
 
 	/*
 	 * CHAIN events only work when paired with an adjacent counter, and it
-- 
2.40.0.348.gf938b09366-goog