linux-kernel - [PATCH v4 3/9] perf record --off-cpu: Parse offcpu-time event

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Message-ID: <20240807153843.3231451-4-howardchu95@gmail.com>
Date: Wed,  7 Aug 2024 23:38:37 +0800
From: Howard Chu <howardchu95@...il.com>
To: namhyung@...nel.org
Cc: irogers@...gle.com,
	acme@...nel.org,
	adrian.hunter@...el.com,
	jolsa@...nel.org,
	kan.liang@...ux.intel.com,
	linux-perf-users@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v4 3/9] 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 | 55 ++++++++++++++++++++---------------
 tools/perf/util/evsel.c       |  2 +-
 2 files changed, 32 insertions(+), 25 deletions(-)

diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
index 1e0e454bfb5e..fae0bb8aaa13 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"
 
@@ -38,39 +39,24 @@ union off_cpu_data {
 
 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);
+	char off_cpu_event[64];
 
-	if (evname == NULL)
-		return -ENOMEM;
-
-	evsel = evsel__new(&attr);
-	if (!evsel) {
-		free(evname);
-		return -ENOMEM;
+	/* after parsing off-cpu event, we'll specify its sample_type in evsel__config() */
+	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->bss->has_cpu && !skel->bss->has_task &&
@@ -86,6 +72,27 @@ 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/evsel.c b/tools/perf/util/evsel.c
index b961467133cf..ccd3bda02b5d 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -1379,7 +1379,7 @@ void evsel__config(struct evsel *evsel, struct record_opts *opts,
 		evsel__reset_sample_bit(evsel, BRANCH_STACK);
 
 	if (evsel__is_offcpu_event(evsel))
-		evsel->core.attr.sample_type &= OFFCPU_SAMPLE_TYPES;
+		evsel->core.attr.sample_type = OFFCPU_SAMPLE_TYPES;
 
 	arch__post_evsel_config(evsel, attr);
 }
-- 
2.45.2