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Commit 48538b58 authored by Mark Rutland's avatar Mark Rutland Committed by Will Deacon
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drivers/perf: arm_pmu: expose a cpumask in sysfs 



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 00e727bb ("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: default avatarMark Rutland <mark.rutland@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
parent 1589680d

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