[PATCH v1 2/2] x86/perf: Export some PMU attributes in caps

[Andi Kleen <andi@firstfloor.org>]

From: Andi Kleen <ak@linux.intel.com>

It can be difficult to figure out for user programs what features
the x86 cpu pmu driver actually supports. Currently it requires
grepping in dmesg, but dmesg is not always available.

This adds a caps directory to /sys/devices/cpu, similar
to the caps already used on intel_pt, which can be used
to discover the available capabilities cleanly.

Currently three capabilities are defined:

- pmu_name
Underlying CPU name known to the driver
- max_precise
Max precise level supported
- branches
Known depth of LBR.

Example:

% grep . /sys/devices/cpu/caps/*
/sys/devices/cpu/caps/branches:32
/sys/devices/cpu/caps/max_precise:3
/sys/devices/cpu/caps/pmu_name:skylake
%

Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/events/core.c       | 34 +++++++++++++++--------
 arch/x86/events/intel/core.c | 66 +++++++++++++++++++++++++++++++++++++++++++-
 arch/x86/events/perf_event.h |  3 ++
 3 files changed, 91 insertions(+), 12 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index af12e294caed..d5f98095a155 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -487,22 +487,28 @@ static inline int precise_br_compat(struct perf_event *event)
 	return m == b;
 }
 
-int x86_pmu_hw_config(struct perf_event *event)
+int x86_pmu_max_precise(void)
 {
-	if (event->attr.precise_ip) {
-		int precise = 0;
+	int precise = 0;
+
+	/* Support for constant skid */
+	if (x86_pmu.pebs_active && !x86_pmu.pebs_broken) {
+		precise++;
 
-		/* Support for constant skid */
-		if (x86_pmu.pebs_active && !x86_pmu.pebs_broken) {
+		/* Support for IP fixup */
+		if (x86_pmu.lbr_nr || x86_pmu.intel_cap.pebs_format >= 2)
 			precise++;
 
-			/* Support for IP fixup */
-			if (x86_pmu.lbr_nr || x86_pmu.intel_cap.pebs_format >= 2)
-				precise++;
+		if (x86_pmu.pebs_prec_dist)
+			precise++;
+	}
+	return precise;
+}
 
-			if (x86_pmu.pebs_prec_dist)
-				precise++;
-		}
+int x86_pmu_hw_config(struct perf_event *event)
+{
+	if (event->attr.precise_ip) {
+		int precise = x86_pmu_max_precise();
 
 		if (event->attr.precise_ip > precise)
 			return -EOPNOTSUPP;
@@ -1752,6 +1758,10 @@ ssize_t x86_event_sysfs_show(char *page, u64 config, u64 event)
 
 static struct attribute_group x86_pmu_attr_group;
 
+static struct attribute_group x86_pmu_caps_group = {
+	.name = "caps",
+};
+
 static int __init init_hw_perf_events(void)
 {
 	struct x86_pmu_quirk *quirk;
@@ -1798,6 +1808,7 @@ static int __init init_hw_perf_events(void)
 				   0, x86_pmu.num_counters, 0, 0);
 
 	x86_pmu_format_group.attrs = x86_pmu.format_attrs;
+	x86_pmu_caps_group.attrs = x86_pmu.caps_attrs;
 
 	if (x86_pmu.event_attrs)
 		x86_pmu_events_group.attrs = x86_pmu.event_attrs;
@@ -2217,6 +2228,7 @@ static const struct attribute_group *x86_pmu_attr_groups[] = {
 	&x86_pmu_attr_group,
 	&x86_pmu_format_group,
 	&x86_pmu_events_group,
+	&x86_pmu_caps_group,
 	NULL,
 };
 
diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
index 82faeed30135..a46bf78c0105 100644
--- a/arch/x86/events/intel/core.c
+++ b/arch/x86/events/intel/core.c
@@ -3795,6 +3795,46 @@ static ssize_t freeze_on_smi_store(struct device *cdev,
 
 static DEVICE_ATTR_RW(freeze_on_smi);
 
+static ssize_t branches_show(struct device *cdev,
+			     struct device_attribute *attr,
+			     char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%d\n", x86_pmu.lbr_nr);
+}
+
+static DEVICE_ATTR_RO(branches);
+
+static struct attribute *lbr_attrs[] = {
+	&dev_attr_branches.attr,
+	NULL
+};
+
+static char pmu_name_str[30];
+
+static ssize_t pmu_name_show(struct device *cdev,
+			     struct device_attribute *attr,
+			     char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%s\n", pmu_name_str);
+}
+
+static DEVICE_ATTR_RO(pmu_name);
+
+static ssize_t max_precise_show(struct device *cdev,
+				  struct device_attribute *attr,
+				  char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%d\n", x86_pmu_max_precise());
+}
+
+static DEVICE_ATTR_RO(max_precise);
+
+static struct attribute *intel_pmu_caps_attrs[] = {
+	&dev_attr_pmu_name.attr,
+	&dev_attr_max_precise.attr,
+	NULL
+};
+
 static struct attribute *intel_pmu_attrs[] = {
 	&dev_attr_freeze_on_smi.attr,
 	NULL,
@@ -3810,6 +3850,7 @@ __init int intel_pmu_init(void)
 	struct extra_reg *er;
 	int version, i;
 	struct attribute **extra_attr = NULL;
+	char *name;
 
 	if (!cpu_has(&boot_cpu_data, X86_FEATURE_ARCH_PERFMON)) {
 		switch (boot_cpu_data.x86) {
@@ -3877,6 +3918,7 @@ __init int intel_pmu_init(void)
 	switch (boot_cpu_data.x86_model) {
 	case INTEL_FAM6_CORE_YONAH:
 		pr_cont("Core events, ");
+		name = "core";
 		break;
 
 	case INTEL_FAM6_CORE2_MEROM:
@@ -3892,6 +3934,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.event_constraints = intel_core2_event_constraints;
 		x86_pmu.pebs_constraints = intel_core2_pebs_event_constraints;
 		pr_cont("Core2 events, ");
+		name = "core2";
 		break;
 
 	case INTEL_FAM6_NEHALEM:
@@ -3923,6 +3966,7 @@ __init int intel_pmu_init(void)
 		extra_attr = nhm_format_attr;
 
 		pr_cont("Nehalem events, ");
+		name = "nehalem";
 		break;
 
 	case INTEL_FAM6_ATOM_PINEVIEW:
@@ -3939,6 +3983,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.pebs_constraints = intel_atom_pebs_event_constraints;
 		x86_pmu.pebs_aliases = intel_pebs_aliases_core2;
 		pr_cont("Atom events, ");
+		name = "bonnell";
 		break;
 
 	case INTEL_FAM6_ATOM_SILVERMONT1:
@@ -3958,6 +4003,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.cpu_events = slm_events_attrs;
 		extra_attr = slm_format_attr;
 		pr_cont("Silvermont events, ");
+		name = "silvermont";
 		break;
 
 	case INTEL_FAM6_ATOM_GOLDMONT:
@@ -3984,6 +4030,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.cpu_events = glm_events_attrs;
 		extra_attr = slm_format_attr;
 		pr_cont("Goldmont events, ");
+		name = "goldmont";
 		break;
 
 	case INTEL_FAM6_ATOM_GEMINI_LAKE:
@@ -4011,6 +4058,7 @@ __init int intel_pmu_init(void)
 		event_attr_td_total_slots_scale_glm.event_str = "4";
 		extra_attr = slm_format_attr;
 		pr_cont("Goldmont plus events, ");
+		name = "goldmont_plus";
 		break;
 
 	case INTEL_FAM6_WESTMERE:
@@ -4041,6 +4089,7 @@ __init int intel_pmu_init(void)
 		intel_pmu_pebs_data_source_nhm();
 		extra_attr = nhm_format_attr;
 		pr_cont("Westmere events, ");
+		name = "westmere";
 		break;
 
 	case INTEL_FAM6_SANDYBRIDGE:
@@ -4079,6 +4128,7 @@ __init int intel_pmu_init(void)
 		extra_attr = nhm_format_attr;
 
 		pr_cont("SandyBridge events, ");
+		name = "sandybridge";
 		break;
 
 	case INTEL_FAM6_IVYBRIDGE:
@@ -4115,6 +4165,7 @@ __init int intel_pmu_init(void)
 		extra_attr = nhm_format_attr;
 
 		pr_cont("IvyBridge events, ");
+		name = "ivybridge";
 		break;
 
 
@@ -4145,6 +4196,7 @@ __init int intel_pmu_init(void)
 		extra_attr = boot_cpu_has(X86_FEATURE_RTM) ?
 			hsw_format_attr : nhm_format_attr;
 		pr_cont("Haswell events, ");
+		name = "haswell";
 		break;
 
 	case INTEL_FAM6_BROADWELL_CORE:
@@ -4183,6 +4235,7 @@ __init int intel_pmu_init(void)
 		extra_attr = boot_cpu_has(X86_FEATURE_RTM) ?
 			hsw_format_attr : nhm_format_attr;
 		pr_cont("Broadwell events, ");
+		name = "broadwell";
 		break;
 
 	case INTEL_FAM6_XEON_PHI_KNL:
@@ -4202,6 +4255,7 @@ __init int intel_pmu_init(void)
 		x86_pmu.flags |= PMU_FL_NO_HT_SHARING;
 		extra_attr = slm_format_attr;
 		pr_cont("Knights Landing/Mill events, ");
+		name = "knights-landing";
 		break;
 
 	case INTEL_FAM6_SKYLAKE_MOBILE:
@@ -4236,6 +4290,7 @@ __init int intel_pmu_init(void)
 		extra_attr = merge_attr(extra_attr, skl_format_attr);
 		x86_pmu.cpu_events = hsw_events_attrs;
 		pr_cont("Skylake events, ");
+		name = "skylake";
 		break;
 
 	default:
@@ -4243,6 +4298,7 @@ __init int intel_pmu_init(void)
 		case 1:
 			x86_pmu.event_constraints = intel_v1_event_constraints;
 			pr_cont("generic architected perfmon v1, ");
+			name = "generic_arch_v1";
 			break;
 		default:
 			/*
@@ -4250,10 +4306,13 @@ __init int intel_pmu_init(void)
 			 */
 			x86_pmu.event_constraints = intel_gen_event_constraints;
 			pr_cont("generic architected perfmon, ");
+			name = "generic_arch_v2+";
 			break;
 		}
 	}
 
+	snprintf(pmu_name_str, sizeof pmu_name_str, "%s", name);
+
 	if (version >= 2 && extra_attr) {
 		x86_pmu.format_attrs = merge_attr(intel_arch3_formats_attr,
 						  extra_attr);
@@ -4306,8 +4365,13 @@ __init int intel_pmu_init(void)
 			x86_pmu.lbr_nr = 0;
 	}
 
-	if (x86_pmu.lbr_nr)
+	x86_pmu.caps_attrs = intel_pmu_caps_attrs;
+
+	if (x86_pmu.lbr_nr) {
+		x86_pmu.caps_attrs = merge_attr(x86_pmu.caps_attrs, lbr_attrs);
 		pr_cont("%d-deep LBR, ", x86_pmu.lbr_nr);
+	}
+
 	/*
 	 * Access extra MSR may cause #GP under certain circumstances.
 	 * E.g. KVM doesn't support offcore event
diff --git a/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
index 476aec3a4cab..e3d38b1cda56 100644
--- a/arch/x86/events/perf_event.h
+++ b/arch/x86/events/perf_event.h
@@ -558,6 +558,7 @@ struct x86_pmu {
 	int		attr_rdpmc;
 	struct attribute **format_attrs;
 	struct attribute **event_attrs;
+	struct attribute **caps_attrs;
 
 	ssize_t		(*events_sysfs_show)(char *page, u64 config);
 	struct attribute **cpu_events;
@@ -741,6 +742,8 @@ int x86_reserve_hardware(void);
 
 void x86_release_hardware(void);
 
+int x86_pmu_max_precise(void);
+
 void hw_perf_lbr_event_destroy(struct perf_event *event);
 
 int x86_setup_perfctr(struct perf_event *event);
-- 
2.9.4