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SubjectRe: [PATCH 4/8] perf evsel: Do not rely on errno values for precise_ip fallback
Thank you very much! Just wondering, would it maybe worth to backport 
the fix to stable kernel too?

В Пн, июл 8, 2019 at 12:42, Arnaldo Carvalho de Melo
<acme@kernel.org> написал:
> From: Jiri Olsa <jolsa@kernel.org>
>
> Konstantin reported problem with default perf record command, which
> fails on some AMD servers, because of the default maximum precise
> config.
>
> The current fallback mechanism counts on getting ENOTSUP errno for
> precise_ip fails, but that's not the case on some AMD servers.
>
> We can fix this by removing the errno check completely, because the
> precise_ip fallback is separated. We can just try (if requested by
> evsel->precise_max) all possible precise_ip, and if one succeeds we
> win,
> if not, we continue with standard fallback.
>
> Reported-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
> Signed-off-by: Jiri Olsa <jolsa@kernel.org>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Cc: Andi Kleen <ak@linux.intel.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Quentin Monnet <quentin.monnet@netronome.com>
> Cc: Kim Phillips <kim.phillips@amd.com>
> Link: http://lkml.kernel.org/r/20190703080949.10356-1-jolsa@kernel.org
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> ---
> tools/perf/util/evsel.c | 10 ++--------
> 1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index 4a5947625c5c..69beb9f80f07 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -1785,14 +1785,8 @@ static int perf_event_open(struct perf_evsel
> *evsel,
> if (fd >= 0)
> break;
>
> - /*
> - * Do quick precise_ip fallback if:
> - * - there is precise_ip set in perf_event_attr
> - * - maximum precise is requested
> - * - sys_perf_event_open failed with ENOTSUP error,
> - * which is associated with wrong precise_ip
> - */
> - if (!precise_ip || !evsel->precise_max || (errno != ENOTSUP))
> + /* Do not try less precise if not requested. */
> + if (!evsel->precise_max)
> break;
>
> /*
> --
> 2.20.1
>


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