Re: [PATCH V2] perf top: Use evsel's cpus to replace user_requested_cpus

[Ian Rogers]

On Tue, Dec 12, 2023 at 11:39 AM <kan.liang@xxxxxxxxxxxxxxx> wrote:
>
> From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
>
> perf top errors out on a hybrid machine
>  $perf top
>
>  Error:
>  The cycles:P event is not supported.
>
> The perf top expects that the "cycles" is collected on all CPUs in the
> system. But for hybrid there is no single "cycles" event which can cover
> all CPUs. Perf has to split it into two cycles events, e.g.,
> cpu_core/cycles/ and cpu_atom/cycles/. Each event has its own CPU mask.
> If a event is opened on the unsupported CPU. The open fails. That's the
> reason of the above error out.
>
> Perf should only open the cycles event on the corresponding CPU. The
> commit ef91871c960e ("perf evlist: Propagate user CPU maps intersecting
> core PMU maps") intersect the requested CPU map with the CPU map of the
> PMU. Use the evsel's cpus to replace user_requested_cpus.
>
> The evlist's threads are also propagated to the evsel's threads in
> __perf_evlist__propagate_maps(). For a system-wide event, perf appends
> a dummy event and assign it to the evsel's threads. For a per-thread
> event, the evlist's thread_map is assigned to the evsel's threads. The
> same as the other tools, e.g., perf record, using the evsel's threads
> when opening an event.
>
> Reported-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Closes: https://lore.kernel.org/linux-perf-users/ZXNnDrGKXbEELMXV@xxxxxxxxxx/
> Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>
> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> ---
>
> Changes since V1:
> - Update the description
> - Add Reviewed-by from Ian

Thanks Kan, quick question. Does "perf top" on hybrid ask the user to
select between the cycles event on cpu_atom and cpu_core? I'm
wondering if there is some kind of missing "hybrid-merge"
functionality like we have for perf stat.

Thanks,
Ian

>  tools/perf/builtin-top.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
> index ea8c7eca5eee..cce9350177e2 100644
> --- a/tools/perf/builtin-top.c
> +++ b/tools/perf/builtin-top.c
> @@ -1027,8 +1027,8 @@ static int perf_top__start_counters(struct perf_top *top)
>
>         evlist__for_each_entry(evlist, counter) {
>  try_again:
> -               if (evsel__open(counter, top->evlist->core.user_requested_cpus,
> -                                    top->evlist->core.threads) < 0) {
> +               if (evsel__open(counter, counter->core.cpus,
> +                               counter->core.threads) < 0) {
>
>                         /*
>                          * Specially handle overwrite fall back.
> --
> 2.35.1
>