[PATCH 42/46] perf record: Toggle overwrite ring buffer for reading

[Wang Nan]

Reading from a overwrite ring buffer is unrelible.
perf_evlist__channel_toggle_paused() should be called before
reading from them.

Toggel overwrite_evt_paused director after receiving done or switch
output.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Signed-off-by: He Kuang <hekuang@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@xxxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
---
 tools/perf/builtin-record.c | 79 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index a069f75..8d247cf 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -40,6 +40,11 @@
 #include <sys/mman.h>
 #include <asm/bug.h>
 
+enum overwrite_evt_state {
+	OVERWRITE_EVT_RUNNING,
+	OVERWRITE_EVT_DATA_PENDING,
+	OVERWRITE_EVT_EMPTY,
+};
 
 struct record {
 	struct perf_tool	tool;
@@ -58,6 +63,7 @@ struct record {
 	bool			buildid_all;
 	bool			timestamp_filename;
 	bool			switch_output;
+	enum overwrite_evt_state overwrite_evt_state;
 	unsigned long long	samples;
 };
 
@@ -389,6 +395,7 @@ try_again:
 
 	session->evlist = evlist;
 	perf_session__set_id_hdr_size(session);
+	rec->overwrite_evt_state = OVERWRITE_EVT_RUNNING;
 out:
 	return rc;
 }
@@ -469,6 +476,52 @@ static struct perf_event_header finished_round_event = {
 	.type = PERF_RECORD_FINISHED_ROUND,
 };
 
+static void
+record__toggle_overwrite_evsels(struct record *rec,
+				enum overwrite_evt_state state)
+{
+	struct perf_evlist *evlist = rec->evlist;
+	enum overwrite_evt_state old_state = rec->overwrite_evt_state;
+	enum action {
+		NONE,
+		PAUSE,
+		RESUME,
+	} action = NONE;
+	int ch, nr_channels;
+
+	switch (old_state) {
+	case OVERWRITE_EVT_RUNNING:
+		if (state != OVERWRITE_EVT_RUNNING)
+			action = PAUSE;
+		break;
+	case OVERWRITE_EVT_DATA_PENDING:
+		if (state == OVERWRITE_EVT_RUNNING)
+			action = RESUME;
+		break;
+	case OVERWRITE_EVT_EMPTY:
+		if (state == OVERWRITE_EVT_RUNNING)
+			action = RESUME;
+		if (state == OVERWRITE_EVT_DATA_PENDING)
+			state = OVERWRITE_EVT_EMPTY;
+		break;
+	default:
+		WARN_ONCE(1, "Shouldn't get there\n");
+	}
+
+	rec->overwrite_evt_state = state;
+
+	if (action == NONE)
+		return;
+
+	nr_channels = perf_evlist__channel_nr(evlist);
+	for (ch = 0; ch < nr_channels; ch++) {
+		if (!perf_evlist__channel_check(evlist, ch, RDONLY))
+			continue;
+		perf_evlist__channel_toggle_paused(evlist, ch,
+						   action == PAUSE);
+	}
+}
+
 static bool record__mmap_should_read(struct record *rec, int idx)
 {
 	int channel = -1;
@@ -513,6 +566,8 @@ static int record__mmap_read_all(struct record *rec)
 	if (bytes_written != rec->bytes_written)
 		rc = record__write(rec, &finished_round_event, sizeof(finished_round_event));
 
+	if (rec->overwrite_evt_state == OVERWRITE_EVT_DATA_PENDING)
+		record__toggle_overwrite_evsels(rec, OVERWRITE_EVT_EMPTY);
 out:
 	return rc;
 }
@@ -872,6 +927,17 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
 	for (;;) {
 		unsigned long long hits = rec->samples;
 
+		/*
+		 * rec->overwrite_evt_state is possible to be
+		 * OVERWRITE_EVT_EMPTY here: when done == true and
+		 * hits != rec->samples after previous reading.
+		 *
+		 * record__toggle_overwrite_evsels ensure we never
+		 * convert OVERWRITE_EVT_EMPTY to OVERWRITE_EVT_DATA_PENDING.
+		 */
+		if (switch_output_started || done || draining)
+			record__toggle_overwrite_evsels(rec, OVERWRITE_EVT_DATA_PENDING);
+
 		if (record__mmap_read_all(rec) < 0) {
 			auxtrace_snapshot_disable();
 			err = -1;
@@ -890,7 +956,20 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
 		}
 
 		if (switch_output_started) {
+			/*
+			 * SIGUSR2 raise after or during record__mmap_read_all().
+			 * continue to read again.
+			 */
+			if (rec->overwrite_evt_state == OVERWRITE_EVT_RUNNING)
+				continue;
+
 			switch_output_started = 0;
+			/*
+			 * Reenable events in overwrite ring buffer after
+			 * record__mmap_read_all(): we should have collected
+			 * data from it.
+			 */
+			record__toggle_overwrite_evsels(rec, OVERWRITE_EVT_RUNNING);
 
 			if (!quiet)
 				fprintf(stderr, "[ perf record: dump data: Woken up %ld times ]\n",
-- 
1.8.3.4