[PATCH 08/23] perf/x86: Export available PMU counters to sysfs

[Zide Chen]

With PMU partitioning support, the set of PMU counters available to a
PMU can vary from the architectural maximum. While this information is
available through CPUID, it is not easily consumable from scripts.

Add two new sysfs ABI files, gp_counters and fixed_counters, under the
PMU caps group to export the available counters. The fixed_counters
file is omitted when the PMU does not support fixed-function counters.

  $ grep . /sys/devices/cpu/caps/*_counters
  /sys/devices/cpu/caps/fixed_counters:0-3
  /sys/devices/cpu/caps/gp_counters:0-7

Suggested-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Signed-off-by: Zide Chen <zide.chen@xxxxxxxxx>
---
 .../sysfs-bus-event_source-devices-caps       |  5 +++
 arch/x86/events/core.c                        | 37 +++++++++++++++++++
 2 files changed, 42 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-bus-event_source-devices-caps b/Documentation/ABI/testing/sysfs-bus-event_source-devices-caps
index a5f506f7d481..385ad7a23dd6 100644
--- a/Documentation/ABI/testing/sysfs-bus-event_source-devices-caps
+++ b/Documentation/ABI/testing/sysfs-bus-event_source-devices-caps
@@ -22,3 +22,8 @@ Description:
 		of PERF_SAMPLE_BRANCH_COUNTERS, while the "branch_counter_width"
 		exposes the width of each counter. Both of them can be used by
 		the perf tool to parse the logged counters in each branch.
+
+		The "gp_counters" and "fixed_counters" attributes expose the
+		available general-purpose and fixed-function PMU counters as
+		a range list, e.g. "0-7". The "fixed_counters" attribute is
+		omitted if the PMU does not support fixed-function counters.
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 76af9cfaf0ad..282170f7c1e1 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2814,14 +2814,51 @@ static ssize_t max_precise_show(struct device *cdev,
 
 static DEVICE_ATTR_RO(max_precise);
 
+static ssize_t gp_counters_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct pmu *pmu = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%*pbl\n", INTEL_PMC_MAX_GENERIC,
+			  hybrid(pmu, cntr_mask));
+}
+
+static ssize_t fixed_counters_show(struct device *dev,
+				   struct device_attribute *attr, char *buf)
+{
+	struct pmu *pmu = dev_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%*pbl\n", INTEL_PMC_MAX_FIXED,
+			  hybrid(pmu, fixed_cntr_mask));
+}
+
+static DEVICE_ATTR_RO(gp_counters);
+static DEVICE_ATTR_RO(fixed_counters);
+
+static umode_t x86_pmu_caps_is_visible(struct kobject *kobj,
+				       struct attribute *attr, int n)
+{
+	struct device *dev = kobj_to_dev(kobj);
+	struct pmu *pmu = dev_get_drvdata(dev);
+
+	if (attr == &dev_attr_fixed_counters.attr &&
+	    !hybrid(pmu, fixed_cntr_mask64))
+		return 0;
+
+	return attr->mode;
+}
+
 static struct attribute *x86_pmu_caps_attrs[] = {
 	&dev_attr_max_precise.attr,
+	&dev_attr_gp_counters.attr,
+	&dev_attr_fixed_counters.attr,
 	NULL
 };
 
 static struct attribute_group x86_pmu_caps_group __ro_after_init = {
 	.name = "caps",
 	.attrs = x86_pmu_caps_attrs,
+	.is_visible = x86_pmu_caps_is_visible,
 };
 
 static const struct attribute_group *x86_pmu_attr_groups[] = {
-- 
2.55.0