Re: [PATCH] perf record: Add a dummy event for a hybrid system

From: Namhyung Kim
Date: Fri Jul 09 2021 - 01:34:52 EST


On Thu, Jul 8, 2021 at 9:05 AM <kan.liang@xxxxxxxxx> wrote:
>
> From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
>
> Some symbols may not be resolved if a user only monitor one type of PMU.
>
> $ sudo perf record -e cpu_atom/branch-instructions/ ./big_small_workload
> $ sudo perf report –stdio
> # Overhead Command Shared Object Symbol
> # ........ ......... .................
> # ......................................
> #
> 28.02% perf-exec [unknown] [.] 0x0000000000401cf6
> 11.32% perf-exec [unknown] [.] 0x0000000000401d04
> 10.90% perf-exec [unknown] [.] 0x0000000000401d11
> 10.61% perf-exec [unknown] [.] 0x0000000000401cfc
>
> To parse symbols, the side-band events, e.g., COMM, which are generated
> by the kernel are required. To decide whether to generate the side-band
> event, the kernel relies on the event_filter_match() to filter the
> unrelated events. On a hybrid system, the event_filter_match() further
> checks the CPU mask of the current enabled PMU. If an event is collected
> on the CPU which doesn't have an enabled PMU, it's treated as an
> unrelated event.
>
> The "big_small_workload" is created in a big core, but runs on a small
> core. The side-band events are filtered, because the user only monitors
> the PMU of the small core. The big core PMU is not enabled.
>
> For a hybrid system, a dummy event is required to generate the complete
> side-band events.
>
> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

Acked-by: Namhyung Kim <namhyung@xxxxxxxxxx>

Thanks,
Namhyung


> ---
> tools/perf/builtin-record.c | 9 +++++----
> 1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index 3337b5f..99607b9 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -891,11 +891,12 @@ static int record__open(struct record *rec)
> int rc = 0;
>
> /*
> - * For initial_delay or system wide, we need to add a dummy event so
> - * that we can track PERF_RECORD_MMAP to cover the delay of waiting or
> - * event synthesis.
> + * For initial_delay or system wide or a hybrid system, we need to
> + * add a dummy event so that we can track PERF_RECORD_MMAP to cover
> + * the delay of waiting or event synthesis.
> */
> - if (opts->initial_delay || target__has_cpu(&opts->target)) {
> + if (opts->initial_delay || target__has_cpu(&opts->target) ||
> + perf_pmu__has_hybrid()) {
> pos = evlist__get_tracking_event(evlist);
> if (!evsel__is_dummy_event(pos)) {
> /* Set up dummy event. */
> --
> 2.7.4
>