[PATCH 2/3] perf: arm_pmu: Only show online CPUs in device's "cpus" attribute

[Yicong Yang]

From: Yicong Yang <yangyicong@xxxxxxxxxxxxx>

When there're CPUs offline after system booting, perf will failed:
[root@localhost ~]# /home/yang/perf stat -a -e armv8_pmuv3_0/cycles/
Error:
The sys_perf_event_open() syscall returned with 19 (No such device) for event (cpu-clock).
/bin/dmesg | grep -i perf may provide additional information.

This is due to PMU's "cpus" is not updated and still contains offline
CPUs and perf will try to open perf event on the offlined CPUs.

Make "cpus" attribute only shows online CPUs and introduced a new
"supported_cpus" where users can get the range of the CPUs this
PMU supported monitoring.

Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
---
 drivers/perf/arm_pmu.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/perf/arm_pmu.c b/drivers/perf/arm_pmu.c
index 8458fe2cebb4..acbb0e1d0414 100644
--- a/drivers/perf/arm_pmu.c
+++ b/drivers/perf/arm_pmu.c
@@ -558,13 +558,35 @@ static ssize_t cpus_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);
+	cpumask_var_t mask;
+	ssize_t n;
+
+	/* If allocation failed then show the supported_cpus */
+	if (!alloc_cpumask_var(&mask, GFP_KERNEL))
+		return cpumap_print_to_pagebuf(true, buf, &armpmu->supported_cpus);
+
+	cpumask_and(mask, &armpmu->supported_cpus, cpu_online_mask);
+	n = cpumap_print_to_pagebuf(true, buf, mask);
+	free_cpumask_var(mask);
+
+	return n;
 }
 
 static DEVICE_ATTR_RO(cpus);
 
+static ssize_t supported_cpus_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_RO(supported_cpus);
+
 static struct attribute *armpmu_common_attrs[] = {
 	&dev_attr_cpus.attr,
+	&dev_attr_supported_cpus.attr,
 	NULL,
 };
 
-- 
2.24.0