linux-kernel - [PATCH v7 04/10] perf record --off-cpu: Preparation of off-cpu BPF program

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Message-ID: <20241108204137.2444151-5-howardchu95@gmail.com>
Date: Fri,  8 Nov 2024 12:41:31 -0800
From: Howard Chu <howardchu95@...il.com>
To: acme@...nel.org,
	peterz@...radead.org
Cc: namhyung@...nel.org,
	irogers@...gle.com,
	mingo@...hat.com,
	mark.rutland@....com,
	james.clark@...aro.org,
	alexander.shishkin@...ux.intel.com,
	jolsa@...nel.org,
	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 v7 04/10] perf record --off-cpu: Preparation of off-cpu BPF program

Set the perf_event map in BPF for dumping off-cpu samples.

Set the offcpu_thresh to specify the threshold.

Signed-off-by: Howard Chu <howardchu95@...il.com>
---
 tools/perf/util/bpf_off_cpu.c          | 20 ++++++++++++++++++++
 tools/perf/util/bpf_skel/off_cpu.bpf.c |  2 ++
 2 files changed, 22 insertions(+)

diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
index 558c5e5c2dc3..cfe5b17393e9 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"
 
@@ -73,6 +74,23 @@ static void off_cpu_start(void *arg)
 		bpf_map_update_elem(fd, &pid, &val, BPF_ANY);
 	}
 
+	/* update BPF perf_event map */
+	evsel = evlist__find_evsel_by_str(evlist, OFFCPU_EVENT);
+	if (evsel == NULL) {
+		pr_err("%s evsel not found\n", OFFCPU_EVENT);
+		return;
+	}
+
+	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, i, 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;
 }
 
@@ -261,6 +279,8 @@ int off_cpu_prepare(struct evlist *evlist, struct target *target,
 		}
 	}
 
+	skel->bss->offcpu_thresh = opts->off_cpu_thresh * 1000;
+
 	err = off_cpu_bpf__attach(skel);
 	if (err) {
 		pr_err("Failed to attach off-cpu BPF skeleton\n");
diff --git a/tools/perf/util/bpf_skel/off_cpu.bpf.c b/tools/perf/util/bpf_skel/off_cpu.bpf.c
index c152116df72f..dc6acafb9353 100644
--- a/tools/perf/util/bpf_skel/off_cpu.bpf.c
+++ b/tools/perf/util/bpf_skel/off_cpu.bpf.c
@@ -97,6 +97,8 @@ const volatile bool uses_cgroup_v1 = false;
 
 int perf_subsys_id = -1;
 
+__u64 offcpu_thresh;
+
 /*
  * Old kernel used to call it task_struct->state and now it's '__state'.
  * Use BPF CO-RE "ignored suffix rule" to deal with it like below:
-- 
2.43.0