[PATCH v1 29/41] perf pmu: Probe supported sample_type flags

[Ian Rogers]

Extend perf_pmu__probe() with probe_sample_types() to test which enum
perf_event_sample_format flags are supported by the PMU.

First test a common bulk sample_type mask with a single
perf_event_open() call to avoid per-bit syscall overhead when all
standard sample flags are supported, and then probe any remaining
PERF_SAMPLE_* bits individually (configuring required companion fields
such as branch_sample_type, sample_regs_user, sample_regs_intr, and
sample_stack_user). Populate probed.sample_types as well as convenience
booleans for branch stack, callchain, data_src, and weight sampling.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/pmu.c | 95 +++++++++++++++++++++++++++++++++++++++++++
 tools/perf/util/pmu.h | 13 ++++++
 2 files changed, 108 insertions(+)

diff --git a/tools/perf/util/pmu.c b/tools/perf/util/pmu.c
index 9033bada9f47..164ed926184e 100644
--- a/tools/perf/util/pmu.c
+++ b/tools/perf/util/pmu.c
@@ -3118,6 +3118,97 @@ static bool try_open_attr_variants(struct perf_event_attr *attr,
 	return false;
 }
 
+/*
+ * Probe which enum perf_event_sample_format flags are supported by @pmu,
+ * testing a common bulk mask first before probing individual flags.
+ */
+static void probe_sample_types(struct perf_pmu *pmu,
+			       const struct perf_event_attr *base_attr,
+			       pid_t pid, int cpu, unsigned long flags)
+{
+	u64 reg_bit = BIT_ULL(perf_arch_reg_ip(EM_HOST)) ?: 1ULL;
+	u64 bulk_mask = PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_TIME |
+			PERF_SAMPLE_ADDR | PERF_SAMPLE_READ | PERF_SAMPLE_CALLCHAIN |
+			PERF_SAMPLE_ID | PERF_SAMPLE_CPU | PERF_SAMPLE_PERIOD |
+			PERF_SAMPLE_STREAM_ID | PERF_SAMPLE_RAW | PERF_SAMPLE_REGS_USER |
+			PERF_SAMPLE_STACK_USER | PERF_SAMPLE_WEIGHT | PERF_SAMPLE_DATA_SRC |
+			PERF_SAMPLE_IDENTIFIER | PERF_SAMPLE_TRANSACTION |
+			PERF_SAMPLE_REGS_INTR | PERF_SAMPLE_CGROUP |
+			PERF_SAMPLE_DATA_PAGE_SIZE | PERF_SAMPLE_CODE_PAGE_SIZE;
+	struct perf_event_attr b_attr = *base_attr;
+	int b_fd;
+
+	b_attr.disabled = 1;
+	b_attr.sample_period = base_attr->sample_period ?: 10000;
+	b_attr.sample_type = bulk_mask;
+	b_attr.sample_regs_user = reg_bit;
+	b_attr.sample_regs_intr = reg_bit;
+	b_attr.sample_stack_user = 64;
+	b_attr.exclude_callchain_kernel = b_attr.exclude_kernel;
+	b_attr.inherit = 0;
+	b_fd = sys_perf_event_open(&b_attr, pid, cpu, -1, flags);
+	if (b_fd >= 0) {
+		close(b_fd);
+		pmu->probed.sample_types |= bulk_mask;
+	}
+
+	for (unsigned int shift = 0; (1ULL << shift) < PERF_SAMPLE_MAX; shift++) {
+		u64 bit = 1ULL << shift;
+		struct perf_event_attr attr = *base_attr;
+		int fd;
+
+		if (pmu->probed.sample_types & bit)
+			continue;
+
+		attr.disabled = 1;
+		attr.sample_period = base_attr->sample_period ?: 10000;
+		attr.sample_type = bit;
+
+		switch (bit) {
+		case PERF_SAMPLE_BRANCH_STACK:
+			attr.branch_sample_type = PERF_SAMPLE_BRANCH_ANY |
+				(attr.exclude_kernel ? PERF_SAMPLE_BRANCH_USER : 0);
+			break;
+		case PERF_SAMPLE_CALLCHAIN:
+			attr.exclude_callchain_kernel = attr.exclude_kernel;
+			break;
+		case PERF_SAMPLE_REGS_USER:
+			attr.sample_regs_user = reg_bit;
+			break;
+		case PERF_SAMPLE_REGS_INTR:
+			attr.sample_regs_intr = reg_bit;
+			break;
+		case PERF_SAMPLE_STACK_USER:
+			attr.sample_stack_user = 64;
+			break;
+		case PERF_SAMPLE_READ:
+			attr.inherit = 0;
+			break;
+		default:
+			break;
+		}
+
+		fd = sys_perf_event_open(&attr, pid, cpu, -1, flags);
+		if (fd < 0 && bit == PERF_SAMPLE_BRANCH_STACK) {
+			attr.branch_sample_type = PERF_SAMPLE_BRANCH_ANY;
+			fd = sys_perf_event_open(&attr, pid, cpu, -1, flags);
+		}
+		if (fd < 0 && bit != PERF_SAMPLE_IP) {
+			attr.sample_type = PERF_SAMPLE_IP | bit;
+			fd = sys_perf_event_open(&attr, pid, cpu, -1, flags);
+		}
+		if (fd >= 0) {
+			close(fd);
+			pmu->probed.sample_types |= bit;
+		}
+	}
+
+	pmu->probed.can_branch_stack = !!(pmu->probed.sample_types & PERF_SAMPLE_BRANCH_STACK);
+	pmu->probed.can_callchain = !!(pmu->probed.sample_types & PERF_SAMPLE_CALLCHAIN);
+	pmu->probed.can_data_src = !!(pmu->probed.sample_types & PERF_SAMPLE_DATA_SRC);
+	pmu->probed.can_weight = !!(pmu->probed.sample_types & PERF_SAMPLE_WEIGHT);
+}
+
 static void __perf_pmu__probe(struct perf_pmu *pmu, int pmu_cpu)
 {
 	struct probe_candidates cands = { .nr = 0 };
@@ -3358,6 +3449,10 @@ static void __perf_pmu__probe(struct perf_pmu *pmu, int pmu_cpu)
 		pmu->probed.can_sample = true;
 	}
 
+	/* 2. All enum perf_event_sample_format types */
+	if (pmu->probed.can_sample)
+		probe_sample_types(pmu, &base_attr, pid, cpu, flags);
+
 	if (keepalive_fd >= 0)
 		close(keepalive_fd);
 	pmu->probed.checked = true;
diff --git a/tools/perf/util/pmu.h b/tools/perf/util/pmu.h
index ddcd28b3cae5..658485faa05d 100644
--- a/tools/perf/util/pmu.h
+++ b/tools/perf/util/pmu.h
@@ -226,10 +226,23 @@ struct perf_pmu {
 		bool can_count;
 		/** @probed.can_sample: Supports interrupt-based sampling (sample_period > 0). */
 		bool can_sample;
+		/** @probed.can_branch_stack: Supports PERF_SAMPLE_BRANCH_STACK. */
+		bool can_branch_stack;
+		/** @probed.can_callchain: Supports PERF_SAMPLE_CALLCHAIN. */
+		bool can_callchain;
+		/** @probed.can_data_src: Supports PERF_SAMPLE_DATA_SRC. */
+		bool can_data_src;
+		/** @probed.can_weight: Supports PERF_SAMPLE_WEIGHT. */
+		bool can_weight;
 		/** @probed.probe_event: Name of the event used to probe the PMU. */
 		char *probe_event;
 		/** @probed.open_err: errno if open_supported is false. */
 		int open_err;
+		/**
+		 * @probed.sample_types: Bitmask of supported
+		 * enum perf_event_sample_format flags.
+		 */
+		u64 sample_types;
 	} probed;
 };
 
-- 
2.56.0.385.gac671c819a-goog