[PATCH 30/91] perf record: Introduce --switch-output-event

Arnaldo Carvalho de Melo
2020-05-06T15:24:43Z

From: Arnaldo Carvalho de Melo <acme@redhat.com>

Now we can use it with --overwrite to have a flight recorder mode that
gets snapshot requests from arbitrary events that are processed in the
side band thread together with the PERF_RECORD_BPF_EVENT processing.

Example:

To collect scheduler events until a recvmmsg syscall happens, system
wide:

[root@five a]# rm -f perf.data.2020042717*
[root@five a]# perf record --overwrite -e sched:*switch,syscalls:*recvmmsg --switch-output-event syscalls:sys_enter_recvmmsg
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2020042717585458 ]
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2020042717590235 ]
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2020042717590398 ]
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Dump perf.data.2020042717590511 ]
[ perf record: Captured and wrote 7.244 MB perf.data.<timestamp> ]

So in the above case we had 3 snapshots, the fourth was forced by
control+C:

[root@five a]# ls -la
total 20440
drwxr-xr-x. 2 root root 4096 Apr 27 17:59 .
dr-xr-x---. 12 root root 4096 Apr 27 17:46 ..
-rw-------. 1 root root 3936125 Apr 27 17:58 perf.data.2020042717585458
-rw-------. 1 root root 5074869 Apr 27 17:59 perf.data.2020042717590235
-rw-------. 1 root root 4291037 Apr 27 17:59 perf.data.2020042717590398
-rw-------. 1 root root 7617037 Apr 27 17:59 perf.data.2020042717590511
[root@five a]#

One can make this more precise by adding the switch output event to the
main -e events list, as since this is done asynchronously, a few events
after the signal event will appear in the snapshots, as can be seen
with:

[root@five a]# rm -f perf.data.20200427175*
[root@five a]# perf record --overwrite -e sched:*switch,syscalls:*recvmmsg --switch-output-event syscalls:sys_enter_recvmmsg
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2020042718024203 ]
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2020042718024301 ]
[ perf record: dump data: Woken up 1 times ]
[ perf record: Dump perf.data.2020042718024484 ]
^C[ perf record: Woken up 1 times to write data ]
[ perf record: Dump perf.data.2020042718024562 ]
[ perf record: Captured and wrote 7.337 MB perf.data.<timestamp> ]
[root@five a]# perf script -i perf.data.2020042718024203 | tail -15
PacerThread 148586 [005] 122.830729: sched:sched_switch: prev_comm=PacerThread prev_pid=148586...
swapper 0 [000] 122.833588: sched:sched_switch: prev_comm=swapper/0 prev_pid=...
NetworkManager 1251 [000] 122.833619: syscalls:sys_enter_recvmmsg: fd: 0x0000001c, mmsg: 0x7ffe83054a1...
swapper 0 [002] 122.833624: sched:sched_switch: prev_comm=swapper/2 prev_pid=...
swapper 0 [003] 122.833624: sched:sched_switch: prev_comm=swapper/3 prev_pid=...
NetworkManager 1251 [000] 122.833626: syscalls:sys_exit_recvmmsg: 0x1
kworker/3:3-eve 158946 [003] 122.833628: sched:sched_switch: prev_comm=kworker/3:3 prev_pid=15894...
swapper 0 [004] 122.833641: sched:sched_switch: prev_comm=swapper/4 prev_pid=...
NetworkManager 1251 [000] 122.833642: sched:sched_switch: prev_comm=NetworkManage...
perf 228273 [002] 122.833645: sched:sched_switch: prev_comm=perf prev_pid=22827...
swapper 0 [011] 122.833646: sched:sched_switch: prev_comm=swapper/1...
swapper 0 [002] 122.833648: sched:sched_switch: prev_comm=swapper/...
kworker/0:2-eve 207387 [000] 122.833648: sched:sched_switch: prev_comm=kworker/0:2 prev_pid=20738...
kworker/2:3-eve 232038 [002] 122.833652: sched:sched_switch: prev_comm=kworker/2:3 prev_pid=23203...
perf 235825 [003] 122.833653: sched:sched_switch: prev_comm=perf prev_pid=23582...
[root@five a]#

Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lore.kernel.org/lkml/20200429131106.27974-8-acme@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
tools/perf/Documentation/perf-record.txt | 13 ++++++++
tools/perf/builtin-record.c | 41 +++++++++++++++++++++---
2 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/tools/perf/Documentation/perf-record.txt b/tools/perf/Documentation/perf-record.txt
index 6e8b4649307c..561ef55743e2 100644
--- a/tools/perf/Documentation/perf-record.txt
+++ b/tools/perf/Documentation/perf-record.txt
@@ -556,6 +556,19 @@ overhead. You can still switch them on with:

--switch-output --no-no-buildid --no-no-buildid-cache

+--switch-output-event::
+Events that will cause the switch of the perf.data file, auto-selecting
+--switch-output=signal, the results are similar as internally the side band
+thread will also send a SIGUSR2 to the main one.
+
+Uses the same syntax as --event, it will just not be recorded, serving only to
+switch the perf.data file as soon as the --switch-output event is processed by
+a separate sideband thread.
+
+This sideband thread is also used to other purposes, like processing the
+PERF_RECORD_BPF_EVENT records as they happen, asking the kernel for extra BPF
+information, etc.
+
--switch-max-files=N::

When rotating perf.data with --switch-output, only keep N files.
diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 5b6a1d23efe5..bb5b4d2fc32b 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -88,7 +88,9 @@ struct record {
struct evlist *evlist;
struct perf_session *session;
struct evlist *sb_evlist;
+ pthread_t thread_id;
int realtime_prio;
+ bool switch_output_event_set;
bool no_buildid;
bool no_buildid_set;
bool no_buildid_cache;
@@ -1437,6 +1439,13 @@ static int record__synthesize(struct record *rec, bool tail)
return err;
}

+static int record__process_signal_event(union perf_event *event __maybe_unused, void *data)
+{
+ struct record *rec = data;
+ pthread_kill(rec->thread_id, SIGUSR2);
+ return 0;
+}
+
static int __cmd_record(struct record *rec, int argc, const char **argv)
{
int err;
@@ -1581,12 +1590,24 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
goto out_child;
}

- if (!opts->no_bpf_event) {
- rec->sb_evlist = evlist__new();
+ if (rec->sb_evlist != NULL) {
+ /*
+ * We get here if --switch-output-event populated the
+ * sb_evlist, so associate a callback that will send a SIGUSR2
+ * to the main thread.
+ */
+ evlist__set_cb(rec->sb_evlist, record__process_signal_event, rec);
+ rec->thread_id = pthread_self();
+ }

+ if (!opts->no_bpf_event) {
if (rec->sb_evlist == NULL) {
- pr_err("Couldn't create side band evlist.\n.");
- goto out_child;
+ rec->sb_evlist = evlist__new();
+
+ if (rec->sb_evlist == NULL) {
+ pr_err("Couldn't create side band evlist.\n.");
+ goto out_child;
+ }
}

if (evlist__add_bpf_sb_event(rec->sb_evlist, &session->header.env)) {
@@ -2180,10 +2201,19 @@ static int switch_output_setup(struct record *rec)
};
unsigned long val;

+ /*
+ * If we're using --switch-output-events, then we imply its
+ * --switch-output=signal, as we'll send a SIGUSR2 from the side band
+ * thread to its parent.
+ */
+ if (rec->switch_output_event_set)
+ goto do_signal;
+
if (!s->set)
return 0;

if (!strcmp(s->str, "signal")) {
+do_signal:
s->signal = true;
pr_debug("switch-output with SIGUSR2 signal\n");
goto enabled;
@@ -2441,6 +2471,9 @@ static struct option __record_options[] = {
&record.switch_output.set, "signal or size[BKMG] or time[smhd]",
"Switch output when receiving SIGUSR2 (signal) or cross a size or time threshold",
"signal"),
+ OPT_CALLBACK_SET(0, "switch-output-event", &record.sb_evlist, &record.switch_output_event_set, "switch output event",
+ "switch output event selector. use 'perf list' to list available events",
+ parse_events_option_new_evlist),
OPT_INTEGER(0, "switch-max-files", &record.switch_output.num_files,
"Limit number of switch output generated files"),
OPT_BOOLEAN(0, "dry-run", &dry_run,
--
2.21.1