drivers/perf: arm_pmu: expose a cpumask in sysfs (48538b58) · Commits · 戴 / test

In systems with heterogeneous CPUs, there are multiple logical CPU PMUs, each of which covers a subset of CPUs in the system. In some cases userspace needs to know which CPUs a given logical PMU covers, so we'd like to expose a cpumask under sysfs, similar to what is done for uncore PMUs. Unfortunately, prior to commit ("perf stat: Balance opening and reading events"), perf stat only correctly handled a cpumask holding a single CPU, and only when profiling in system-wide mode. In other cases, the presence of a cpumask file could cause perf stat to behave erratically. Thus, exposing a cpumask file would break older perf binaries in cases where they would otherwise work. To avoid this issue while still providing userspace with the information it needs, this patch exposes a differently-named file (cpus) under sysfs. New tools can look for this and operate correctly, while older tools will not be adversely affected by its presence. Signed-off-by:

Mark Rutland <mark.rutland@arm.com> Cc: Will Deacon <will.deacon@arm.com> Signed-off-by:

Will Deacon <will.deacon@arm.com>

drivers/perf/arm_pmu.c

+20 −0

Original line number	Diff line number	Diff line
		@@ -534,6 +534,24 @@ static int armpmu_filter_match(struct perf_event *event)
		return cpumask_test_cpu(cpu, &armpmu->supported_cpus);
		}

		static ssize_t armpmu_cpumask_show(struct device *dev,
		struct device_attribute attr, char buf)
		{
		struct arm_pmu *armpmu = to_arm_pmu(dev_get_drvdata(dev));
		return cpumap_print_to_pagebuf(true, buf, &armpmu->supported_cpus);
		}

		static DEVICE_ATTR(cpus, S_IRUGO, armpmu_cpumask_show, NULL);

		static struct attribute *armpmu_common_attrs[] = {
		&dev_attr_cpus.attr,
		NULL,
		};

		static struct attribute_group armpmu_common_attr_group = {
		.attrs = armpmu_common_attrs,
		};

		static void armpmu_init(struct arm_pmu *armpmu)
		{
		atomic_set(&armpmu->active_events, 0);
		@@ -551,6 +569,8 @@ static void armpmu_init(struct arm_pmu *armpmu)
		.filter_match = armpmu_filter_match,
		.attr_groups = armpmu->attr_groups,
		};
		armpmu->attr_groups[ARMPMU_ATTR_GROUP_COMMON] =
		&armpmu_common_attr_group;
		}

		/* Set at runtime when we know what CPU type we are. */

include/linux/perf/arm_pmu.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -78,6 +78,7 @@ struct pmu_hw_events {
		};

		enum armpmu_attr_groups {
		ARMPMU_ATTR_GROUP_COMMON,
		ARMPMU_ATTR_GROUP_EVENTS,
		ARMPMU_ATTR_GROUP_FORMATS,
		ARMPMU_NR_ATTR_GROUPS

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