linux-kernel - [PATCH v6 3/8] perf record --off-cpu: Parse offcpu-time event

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Message-ID: <20240927202736.767941-4-howardchu95@gmail.com>
Date: Fri, 27 Sep 2024 13:27:31 -0700
From: Howard Chu <howardchu95@...il.com>
To: peterz@...radead.org
Cc: mingo@...hat.com,
	acme@...nel.org,
	namhyung@...nel.org,
	mark.rutland@....com,
	alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org,
	irogers@...gle.com,
	adrian.hunter@...el.com,
	kan.liang@...ux.intel.com,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Howard Chu <howardchu95@...il.com>
Subject: [PATCH v6 3/8] perf record --off-cpu: Parse offcpu-time event

Parse offcpu-time event using parse_event, in off_cpu_start(), write
evlist fds got from evlist__open() to perf_event_array BPF map.

Signed-off-by: Howard Chu <howardchu95@...il.com>
---
 tools/perf/util/bpf_off_cpu.c          | 56 +++++++++++++++-----------
 tools/perf/util/bpf_skel/off_cpu.bpf.c |  9 +++++
 2 files changed, 41 insertions(+), 24 deletions(-)

diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
index eaef643f50e3..f7233a09ec77 100644
--- a/tools/perf/util/bpf_off_cpu.c
+++ b/tools/perf/util/bpf_off_cpu.c
@@ -13,6 +13,7 @@
 #include "util/cgroup.h"
 #include "util/strlist.h"
 #include <bpf/bpf.h>
+#include <internal/xyarray.h>
 
 #include "bpf_skel/off_cpu.skel.h"
 
@@ -36,41 +37,27 @@ union off_cpu_data {
 	u64 array[1024 / sizeof(u64)];
 };
 
+u64 off_cpu_raw_data[1024 / sizeof(u64)];
+
 static int off_cpu_config(struct evlist *evlist)
 {
-	struct evsel *evsel;
-	struct perf_event_attr attr = {
-		.type	= PERF_TYPE_SOFTWARE,
-		.config = PERF_COUNT_SW_BPF_OUTPUT,
-		.size	= sizeof(attr), /* to capture ABI version */
-	};
-	char *evname = strdup(OFFCPU_EVENT);
-
-	if (evname == NULL)
-		return -ENOMEM;
+	char off_cpu_event[64];
 
-	evsel = evsel__new(&attr);
-	if (!evsel) {
-		free(evname);
-		return -ENOMEM;
+	scnprintf(off_cpu_event, sizeof(off_cpu_event), "bpf-output/no-inherit=1,name=%s/", OFFCPU_EVENT);
+	if (parse_event(evlist, off_cpu_event)) {
+		pr_err("Failed to open off-cpu event\n");
+		return -1;
 	}
 
-	evsel->core.attr.freq = 1;
-	evsel->core.attr.sample_period = 1;
-	/* off-cpu analysis depends on stack trace */
-	evsel->core.attr.sample_type = PERF_SAMPLE_CALLCHAIN;
-
-	evlist__add(evlist, evsel);
-
-	free(evsel->name);
-	evsel->name = evname;
-
 	return 0;
 }
 
 static void off_cpu_start(void *arg)
 {
 	struct evlist *evlist = arg;
+	struct evsel *evsel;
+	struct perf_cpu pcpu;
+	int i, err;
 
 	/* update task filter for the given workload */
 	if (skel->rodata->has_task && skel->rodata->uses_tgid &&
@@ -84,6 +71,27 @@ static void off_cpu_start(void *arg)
 		bpf_map_update_elem(fd, &pid, &val, BPF_ANY);
 	}
 
+	/* sample id and fds in BPF's perf_event_array can only be set after record__open() */
+	evsel = evlist__find_evsel_by_str(evlist, OFFCPU_EVENT);
+	if (evsel == NULL) {
+		pr_err("%s evsel not found\n", OFFCPU_EVENT);
+		return;
+	}
+
+	if (evsel->core.id)
+		skel->bss->sample_id = evsel->core.id[0];
+
+	perf_cpu_map__for_each_cpu(pcpu, i, evsel->core.cpus) {
+		err = bpf_map__update_elem(skel->maps.offcpu_output,
+					   &pcpu.cpu, sizeof(__u32),
+					   xyarray__entry(evsel->core.fd, pcpu.cpu, 0),
+					   sizeof(__u32), BPF_ANY);
+		if (err) {
+			pr_err("Failed to update perf event map for direct off-cpu dumping\n");
+			return;
+		}
+	}
+
 	skel->bss->enabled = 1;
 }
 
diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
index 5ea320aa9a53..e2a887228fd9 100644
--- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
+++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
@@ -18,6 +18,8 @@
 #define MAX_STACKS   32
 #define MAX_ENTRIES  102400
 
+#define MAX_CPUS  4096
+
 struct tstamp_data {
 	__u32 stack_id;
 	__u32 state;
@@ -39,6 +41,13 @@ struct {
 	__uint(max_entries, MAX_ENTRIES);
 } stacks SEC(".maps");
 
+struct {
+	__uint(type, BPF_MAP_TYPE_PERF_EVENT_ARRAY);
+	__uint(key_size, sizeof(__u32));
+	__uint(value_size, sizeof(__u32));
+	__uint(max_entries, MAX_CPUS);
+} offcpu_output SEC(".maps");
+
 struct {
 	__uint(type, BPF_MAP_TYPE_TASK_STORAGE);
 	__uint(map_flags, BPF_F_NO_PREALLOC);
-- 
2.43.0