[PATCH 3/5] perf record: Tracking side-band events for all CPUs when tracing selected CPUs

[Yang Jihong]

User space tasks can migrate between CPUs, we need to track side-band
events for all CPUs.

The specific scenarios are as follows:

         CPU0                                 CPU1
  perf record -C 0 start
                              taskA starts to be created and executed
                                -> PERF_RECORD_COMM and PERF_RECORD_MMAP
                                   events only deliver to CPU1
                              ......
                                |
                          migrate to CPU0
                                |
  Running on CPU0    <----------/
  ...

  perf record -C 0 stop

Now perf samples the PC of taskA. However, perf does not record the
PERF_RECORD_COMM and PERF_RECORD_COMM events of taskA.
Therefore, the comm and symbols of taskA cannot be parsed.

The sys_perf_event_open invoked is as follows:

  # perf --debug verbose=3 record -e cpu-clock -C 1 true
  <SNIP>
  Opening: cpu-clock
  ------------------------------------------------------------
  perf_event_attr:
    type                             1
    size                             136
    { sample_period, sample_freq }   4000
    sample_type                      IP|TID|TIME|ID|CPU|PERIOD
    read_format                      ID|LOST
    disabled                         1
    inherit                          1
    freq                             1
    sample_id_all                    1
    exclude_guest                    1
  ------------------------------------------------------------
  sys_perf_event_open: pid -1  cpu 1  group_fd -1  flags 0x8 = 5
  Opening: dummy:HG
  ------------------------------------------------------------
  perf_event_attr:
    type                             1
    size                             136
    config                           0x9
    { sample_period, sample_freq }   4000
    sample_type                      IP|TID|TIME|ID|CPU|PERIOD
    read_format                      ID|LOST
    inherit                          1
    mmap                             1
    comm                             1
    freq                             1
    task                             1
    sample_id_all                    1
    mmap2                            1
    comm_exec                        1
    ksymbol                          1
    bpf_event                        1
  ------------------------------------------------------------
  sys_perf_event_open: pid -1  cpu 0  group_fd -1  flags 0x8 = 6
  sys_perf_event_open: pid -1  cpu 1  group_fd -1  flags 0x8 = 7
  sys_perf_event_open: pid -1  cpu 2  group_fd -1  flags 0x8 = 9
  sys_perf_event_open: pid -1  cpu 3  group_fd -1  flags 0x8 = 10
  sys_perf_event_open: pid -1  cpu 4  group_fd -1  flags 0x8 = 11
  sys_perf_event_open: pid -1  cpu 5  group_fd -1  flags 0x8 = 12
  sys_perf_event_open: pid -1  cpu 6  group_fd -1  flags 0x8 = 13
  sys_perf_event_open: pid -1  cpu 7  group_fd -1  flags 0x8 = 14
  <SNIP>

Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
---
 tools/perf/builtin-record.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 8872cd037f2c..69e0d8c75aab 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -908,6 +908,31 @@ static int record__config_off_cpu(struct record *rec)
 	return off_cpu_prepare(rec->evlist, &rec->opts.target, &rec->opts);
 }
 
+static int record__config_tracking_events(struct record *rec)
+{
+	struct evsel *evsel;
+	struct evlist *evlist = rec->evlist;
+	struct record_opts *opts = &rec->opts;
+
+	/*
+	 * User space tasks can migrate between CPUs, so when tracing
+	 * selected CPUs, sideband for all CPUs is still needed.
+	 */
+	if (opts->target.cpu_list) {
+		evsel = evlist__findnew_tracking_event(evlist);
+		if (!evsel)
+			return -ENOMEM;
+
+		if (!evsel->core.system_wide) {
+			evsel->core.system_wide = true;
+			evsel__set_sample_bit(evsel, TIME);
+			perf_evlist__propagate_maps(&evlist->core, &evsel->core);
+		}
+	}
+
+	return 0;
+}
+
 static bool record__kcore_readable(struct machine *machine)
 {
 	char kcore[PATH_MAX];
@@ -4235,6 +4260,12 @@ int cmd_record(int argc, const char **argv)
 		goto out;
 	}
 
+	err = record__config_tracking_events(rec);
+	if (err) {
+		pr_err("record__config_tracking_events failed, error %d\n", err);
+		goto out;
+	}
+
 	err = record__init_thread_masks(rec);
 	if (err) {
 		pr_err("Failed to initialize parallel data streaming masks\n");
-- 
2.30.GIT