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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 00e727bb38 ("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>
This commit is contained in:
Mark Rutland 2016-09-09 14:08:30 +01:00 committed by Will Deacon
parent 1589680da6
commit 48538b5863
2 changed files with 21 additions and 0 deletions
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20
drivers/perf/arm_pmu.c
View File

@ -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. */

1
include/linux/perf/arm_pmu.h
View File

@ -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