[RFC V1 08/11] arm64/perf: Enable branch stack sampling

Anshuman Khandual anshuman.khandual at arm.com
Sun Jan 23 20:30:50 PST 2022


Now that all the required pieces are already in place, just enable the perf
branch stack sampling support on arm64 platform, by removing the gate which
blocks it in armpmu_event_init().

Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: linux-kernel at vger.kernel.org
Cc: linux-arm-kernel at lists.infradead.org
Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
---
 drivers/perf/arm_pmu.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 0800c8858ed8..2117bf5d3232 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -537,9 +537,28 @@ static int armpmu_event_init(struct perf_event *event)
 		!cpumask_test_cpu(event->cpu, &armpmu->supported_cpus))
 		return -ENOENT;
 
-	/* does not support taken branch sampling */
-	if (has_branch_stack(event))
-		return -EOPNOTSUPP;
+	if (has_branch_stack(event)) {
+		/*
+		 * BRBE support is absent. Select CONFIG_ARM_BRBE_PMU
+		 * in the config, before branch stack sampling events
+		 * can be requested.
+		 */
+		if (!IS_ENABLED(CONFIG_ARM_BRBE_PMU)) {
+			pr_warn_once("BRBE is disabled, select CONFIG_ARM_BRBE_PMU\n");
+			return -EOPNOTSUPP;
+		}
+
+		/*
+		 * Branch stack sampling event can not be supported in
+		 * case either the required driver itself is absent or
+		 * BRBE buffer, is not supported. Besides checking for
+		 * the callback prevents a crash in case it's absent.
+		 */
+		if (!armpmu->brbe_supported || !armpmu->brbe_supported(event)) {
+			pr_warn_once("BRBE is not supported\n");
+			return -EOPNOTSUPP;
+		}
+	}
 
 	if (armpmu->map_event(event) == -ENOENT)
 		return -ENOENT;
-- 
2.25.1




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