[PATCH v10 08/10] perf record --off-cpu: Dump the remaining samples in BPF's stack trace map

[Howard Chu]

Dump the remaining samples, as if it is dumping a direct sample.

Put the stack trace, tid, off-cpu time and cgroup id into the raw_data
section, just like a direct off-cpu sample coming from BPF's
bpf_perf_event_output().

This ensures that evsel__parse_sample() correctly parses both direct
samples and accumulated samples.

Suggested-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>
Signed-off-by: Howard Chu <howardchu95@xxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: James Clark <james.clark@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20241108204137.2444151-10-howardchu95@xxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/bpf_off_cpu.c | 59 +++++++++++++++++++++--------------
 1 file changed, 35 insertions(+), 24 deletions(-)

diff --git a/tools/perf/util/bpf_off_cpu.c b/tools/perf/util/bpf_off_cpu.c
index 2378fb5a893f..d6f015362e85 100644
--- a/tools/perf/util/bpf_off_cpu.c
+++ b/tools/perf/util/bpf_off_cpu.c
@@ -37,6 +37,8 @@ union off_cpu_data {
 	u64 array[1024 / sizeof(u64)];
 };
 
+u64 off_cpu_raw[MAX_STACKS + 5];
+
 static int off_cpu_config(struct evlist *evlist)
 {
 	char off_cpu_event[64];
@@ -309,6 +311,7 @@ int off_cpu_write(struct perf_session *session)
 {
 	int bytes = 0, size;
 	int fd, stack;
+	u32 raw_size;
 	u64 sample_type, val, sid = 0;
 	struct evsel *evsel;
 	struct perf_data_file *file = &session->data->file;
@@ -348,46 +351,54 @@ int off_cpu_write(struct perf_session *session)
 
 	while (!bpf_map_get_next_key(fd, &prev, &key)) {
 		int n = 1;  /* start from perf_event_header */
-		int ip_pos = -1;
 
 		bpf_map_lookup_elem(fd, &key, &val);
 
+		/* zero-fill some of the fields, will be overwritten by raw_data when parsing */
 		if (sample_type & PERF_SAMPLE_IDENTIFIER)
 			data.array[n++] = sid;
-		if (sample_type & PERF_SAMPLE_IP) {
-			ip_pos = n;
+		if (sample_type & PERF_SAMPLE_IP)
 			data.array[n++] = 0;  /* will be updated */
-		}
 		if (sample_type & PERF_SAMPLE_TID)
-			data.array[n++] = (u64)key.pid << 32 | key.tgid;
+			data.array[n++] = 0;
 		if (sample_type & PERF_SAMPLE_TIME)
 			data.array[n++] = tstamp;
-		if (sample_type & PERF_SAMPLE_ID)
-			data.array[n++] = sid;
 		if (sample_type & PERF_SAMPLE_CPU)
 			data.array[n++] = 0;
 		if (sample_type & PERF_SAMPLE_PERIOD)
-			data.array[n++] = val;
-		if (sample_type & PERF_SAMPLE_CALLCHAIN) {
-			int len = 0;
-
-			/* data.array[n] is callchain->nr (updated later) */
-			data.array[n + 1] = PERF_CONTEXT_USER;
-			data.array[n + 2] = 0;
-
-			bpf_map_lookup_elem(stack, &key.stack_id, &data.array[n + 2]);
-			while (data.array[n + 2 + len])
+			data.array[n++] = 0;
+		if (sample_type & PERF_SAMPLE_RAW) {
+			/*
+			 *  [ size ][ data ]
+			 *  [     data     ]
+			 *  [     data     ]
+			 *  [     data     ]
+			 *  [ data ][ empty]
+			 */
+			int len = 0, i = 0;
+			void *raw_data = (void *)data.array + n * sizeof(u64);
+
+			off_cpu_raw[i++] = (u64)key.pid << 32 | key.tgid;
+			off_cpu_raw[i++] = val;
+
+			/* off_cpu_raw[i] is callchain->nr (updated later) */
+			off_cpu_raw[i + 1] = PERF_CONTEXT_USER;
+			off_cpu_raw[i + 2] = 0;
+
+			bpf_map_lookup_elem(stack, &key.stack_id, &off_cpu_raw[i + 2]);
+			while (off_cpu_raw[i + 2 + len])
 				len++;
 
-			/* update length of callchain */
-			data.array[n] = len + 1;
+			off_cpu_raw[i] = len + 1;
+			i += len + 2;
+
+			off_cpu_raw[i++] = key.cgroup_id;
 
-			/* update sample ip with the first callchain entry */
-			if (ip_pos >= 0)
-				data.array[ip_pos] = data.array[n + 2];
+			raw_size = i * sizeof(u64) + sizeof(u32); /* 4 bytes for alignment */
+			memcpy(raw_data, &raw_size, sizeof(raw_size));
+			memcpy(raw_data + sizeof(u32), off_cpu_raw, i * sizeof(u64));
 
-			/* calculate sample callchain data array length */
-			n += len + 2;
+			n += i + 1;
 		}
 		if (sample_type & PERF_SAMPLE_CGROUP)
 			data.array[n++] = key.cgroup_id;
-- 
2.43.0