Em Mon, Sep 21, 2015 at 09:26:49AM +0900, Namhyung Kim escreveu:
> When perf creates a new child to profile, the events are enabled on
> exec(). And in this case, it doesn't synthesize any event for the
> child since they'll be generated during exec(). But there's an window
> between the enabling and the event generation.
>
> It used to be overcome since samples are only in kernel (so we always
> have the map) and the comm is overridden by a later COMM event.
> However it won't work if events are processed and displayed before the
> COMM event overrides like in 'perf script'. This leads to those early
> samples (like native_write_msr_safe) not having a comm but pid (like
> ':15328').
>
> So it needs to synthesize COMM event for the child explicitly before
> enabling so that it can have a correct comm. But at this time, the
> comm will be "perf" since it's not exec-ed yet.
>
> Acked-by: Jiri Olsa <[email protected]>
> Signed-off-by: Namhyung Kim <[email protected]>
> ---
> tools/perf/builtin-record.c | 41 ++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 142eeb341b29..b83373adb9f8 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -469,6 +469,43 @@ static void workload_exec_failed_signal(int signo
> __maybe_unused,
> child_finished = 1;
> }
>
> +static int synthesize_workload_comm_event(struct perf_evlist *evlist, void
> *arg)
> +{
> + union perf_event *event;
> + struct record *rec = arg;
> + struct machine *machine = &rec->session->machines.host;
> + int pid = evlist->workload.pid;
> + const char *comm_str = program_invocation_short_name;
> + size_t comm_size, total_size;
> + int ret;
> +
> + comm_size = PERF_ALIGN(strlen(comm_str) + 1, sizeof(u64));
> + total_size = sizeof(event->comm) + machine->id_hdr_size;
> + /*
> + * (aligned) comm size might be smaller than expected size
> + * (i.e. size of event->comm.comm[]), in that case it needs
> + * to shrink the total size.
> + */
> + if (comm_size < sizeof(event->comm.comm))
> + total_size -= sizeof(event->comm.comm) - comm_size;
> +
> + event = zalloc(total_size);
> + if (event == NULL)
> + return -ENOMEM;
> +
> + event->comm.header.type = PERF_RECORD_COMM;
> + event->comm.header.size = total_size;
> +
> + event->comm.pid = pid;
> + event->comm.tid = pid;
> + strncpy(event->comm.comm, comm_str, comm_size);
> +
> + ret = record__write(rec, event, total_size);
> +
> + free(event);
> + return ret;
> +}
> +
> static void snapshot_sig_handler(int sig);
>
> static int __cmd_record(struct record *rec, int argc, const char **argv)
> @@ -637,7 +674,9 @@ static int __cmd_record(struct record *rec, int argc,
> const char **argv)
> * Let the child rip
> */
> if (forks)
> - perf_evlist__start_workload(rec->evlist);
> + perf_evlist__start_workload_ex(rec->evlist,
> + synthesize_workload_comm_event,
> + rec);
Why not call it directly? I.e.:
if (forks) {
err = synthesize_workload_comm_event(evlist, rec);
if (!err)
err = perf_evlist__start_workload(rec->evlist);
}
Since, from what I saw, the very first thing that
perf_evlist__start_workload_ex() does is to call the callback?
Also, don't we have already a synthesize_comm routine? I.e. can't
perf_event__prepare_comm() be used here?
Something like:
union perf_event event;
pid_t tgid, ppid;
err = perf_event__prepare_comm(&event, evlist->workload.pid,
machine, &tgid, &ppid);
if (!err)
err = record__write(rec, &event, sizeof(event.comm));
- Arnaldo
>
> if (opts->initial_delay) {
> usleep(opts->initial_delay * 1000);
> --
> 2.5.0
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