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Date: Wed, 29 Apr 2020 10:25:52 -0700
From: Ian Rogers <irogers@...gle.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Jiri Olsa <jolsa@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
Ingo Molnar <mingo@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Clark Williams <williams@...hat.com>,
LKML <linux-kernel@...r.kernel.org>,
linux-perf-users <linux-perf-users@...r.kernel.org>,
Arnaldo Carvalho de Melo <acme@...hat.com>,
Adrian Hunter <adrian.hunter@...el.com>,
Song Liu <songliubraving@...com>,
Wang Nan <wangnan0@...wei.com>
Subject: Re: [PATCH 7/8] perf record: Introduce --switch-output-event
On Wed, Apr 29, 2020 at 6:14 AM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> From: Arnaldo Carvalho de Melo <acme@...hat.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@...e a]# rm -f perf.data.2020042717*
> [root@...e 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@...e 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@...e 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@...e a]# rm -f perf.data.20200427175*
> [root@...e 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@...e 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@...e a]#
>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Song Liu <songliubraving@...com>
> Cc: Wang Nan <wangnan0@...wei.com>
> Link: http://lore.kernel.org/lkml/20200427211935.25789-8-acme@kernel.org
> Link: http://lore.kernel.org/lkml/20200428121601.GB2245@kernel.org
> Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.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.
I found this paragraph a little hard, perhaps:
A list of events that when they occur cause the output perf.data file
to be ended and a new one created. The signal event,
--switch-output=signal, is auto-selected as SIGUSR2 is used internally
by the thread monitoring the events.
> +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 ed2244847400..7a6a89972691 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -87,7 +87,9 @@ 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;
> @@ -1436,6 +1438,13 @@ 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;
> @@ -1580,12 +1589,24 @@ 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)) {
> @@ -2179,10 +2200,19 @@ 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;
> @@ -2440,6 +2470,9 @@ 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",
Perhaps:
"A list of events, see 'perf list', that when they occur cause the end
of one perf.data file and the creation of another"
Thanks,
Ian
> + 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
>
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