Re: [PATCH] perf tools: Remove evsel__handle_error_quirks()

[Chun-Tse Shao]

On Wed, Apr 9, 2025 at 6:02 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> The evsel__handle_error_quirks() is to fixup invalid event attributes on
> some architecture based on the error code.  Currently it's only used for
> AMD to disable precise_ip not to use IBS which has more restrictions.
>
> But the commit c33aea446bf555ab changed call evsel__precise_ip_fallback
> for any errors so there's no difference with the above function.  To
> make matter worse, it caused a problem with branch stack on Zen3.
>
> The IBS doesn't support branch stack so it should use a regular core
> PMU event.  The default event is set precise_max and it starts with 3.
> And evsel__precise_ip_fallback() tries with it and reduces the level one
> by one.  At last it tries with 0 but it also failed on Zen3 since the
> branch stack is not supported for the cycles event.
>
> At this point, evsel__precise_ip_fallback() restores the original
> precise_ip value (3) in the hope that it can succeed with other modifier
> (like exclude_kernel).  Then evsel__handle_error_quirks() see it has
> precise_ip != 0 and make it retry with 0.  This created an infinite
> loop.
>
> Before:
>
>   $ perf record -b -vv |& grep removing
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   removing precise_ip on AMD
>   ...
>
> After:
>
>   $ perf record -b true
>   Error:
>   Failure to open event 'cycles:P' on PMU 'cpu' which will be removed.
>   Invalid event (cycles:P) in per-thread mode, enable system wide with '-a'.
>   Error:
>   Failure to open any events for recording.
>
> Fixes: c33aea446bf555ab ("perf tools: Fix precise_ip fallback logic")
> Cc: Ravi Bangoria <ravi.bangoria@xxxxxxx>
> Signed-off-by: Namhyung Kim <namhyung@xxxxxxxxxx>
Tested-by: Chun-Tse Shao <ctshao@xxxxxxxxxx>
> ---
>  tools/perf/util/evsel.c | 22 ----------------------
>  1 file changed, 22 deletions(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 1974395492d7da5e..3c030da2e477c707 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2566,25 +2566,6 @@ static bool evsel__detect_missing_features(struct evsel *evsel, struct perf_cpu
>         return false;
>  }
>
> -static bool evsel__handle_error_quirks(struct evsel *evsel, int error)
> -{
> -       /*
> -        * AMD core PMU tries to forward events with precise_ip to IBS PMU
> -        * implicitly.  But IBS PMU has more restrictions so it can fail with
> -        * supported event attributes.  Let's forward it back to the core PMU
> -        * by clearing precise_ip only if it's from precise_max (:P).
> -        */
> -       if ((error == -EINVAL || error == -ENOENT) && x86__is_amd_cpu() &&
> -           evsel->core.attr.precise_ip && evsel->precise_max) {
> -               evsel->core.attr.precise_ip = 0;
> -               pr_debug2_peo("removing precise_ip on AMD\n");
> -               display_attr(&evsel->core.attr);
> -               return true;
> -       }
> -
> -       return false;
> -}
> -
>  static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
>                 struct perf_thread_map *threads,
>                 int start_cpu_map_idx, int end_cpu_map_idx)
> @@ -2730,9 +2711,6 @@ static int evsel__open_cpu(struct evsel *evsel, struct perf_cpu_map *cpus,
>         if (evsel__precise_ip_fallback(evsel))
>                 goto retry_open;
>
> -       if (evsel__handle_error_quirks(evsel, err))
> -               goto retry_open;
> -
>  out_close:
>         if (err)
>                 threads->err_thread = thread;
> --
> 2.49.0.504.g3bcea36a83-goog
>