linux-kernel - Re: [PATCH v3] perf evlist: Fix evlist__new

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Message-ID: <CAM9d7ciSY25Jf-MG24NWJu3aKJWXT2GN43qrV5WCuohLNZn1iw@mail.gmail.com>
Date: Tue, 23 Jan 2024 16:46:43 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: James Clark <james.clark@....com>
Cc: linux-perf-users@...r.kernel.org, irogers@...gle.com, 
	kan.liang@...ux.intel.com, mark.rutland@....com, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
	Jiri Olsa <jolsa@...nel.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	Changbin Du <changbin.du@...wei.com>, Yang Jihong <yangjihong1@...wei.com>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] perf evlist: Fix evlist__new_default() for > 1 core PMU

Hi James,

On Tue, Jan 23, 2024 at 2:39 AM James Clark <james.clark@....com> wrote:
>
> The 'Session topology' test currently fails with this message when
> evlist__new_default() opens more than one event:
>
>   32: Session topology                                                :
>   --- start ---
>   templ file: /tmp/perf-test-vv5YzZ
>   Using CPUID 0x00000000410fd070
>   Opening: unknown-hardware:HG
>   ------------------------------------------------------------
>   perf_event_attr:
>     type                             0 (PERF_TYPE_HARDWARE)
>     config                           0xb00000000
>     disabled                         1
>   ------------------------------------------------------------
>   sys_perf_event_open: pid 0  cpu -1  group_fd -1  flags 0x8 = 4
>   Opening: unknown-hardware:HG
>   ------------------------------------------------------------
>   perf_event_attr:
>     type                             0 (PERF_TYPE_HARDWARE)
>     config                           0xa00000000
>     disabled                         1
>   ------------------------------------------------------------
>   sys_perf_event_open: pid 0  cpu -1  group_fd -1  flags 0x8 = 5
>   non matching sample_type
>   FAILED tests/topology.c:73 can't get session
>   ---- end ----
>   Session topology: FAILED!
>
> This is because when re-opening the file and parsing the header, Perf
> expects that any file that has more than one event has the sample ID
> flag set. Perf record already sets the flag in a similar way when there
> is more than one event, so add the same logic to evlist__new_default().
>
> evlist__new_default() is only currently used in tests, so I don't
> expect this change to have any other side effects. The other tests that
> use it don't save and re-open the file so don't hit this issue.
>
> The session topology test has been failing on Arm big.LITTLE platforms
> since commit 251aa040244a ("perf parse-events: Wildcard most
> "numeric" events") when evlist__new_default() started opening multiple
> events for 'cycles'.
>
> Fixes: 251aa040244a ("perf parse-events: Wildcard most "numeric" events")
> Closes: https://lore.kernel.org/lkml/CAP-5=fWVQ-7ijjK3-w1q+k2WYVNHbAcejb-xY0ptbjRw476VKA@mail.gmail.com/
> Tested-by: Ian Rogers <irogers@...gle.com>
> Reviewed-by: Ian Rogers <irogers@...gle.com>
> Tested-by: Kan Liang <kan.liang@...ux.intel.com>
> Signed-off-by: James Clark <james.clark@....com>
> ---
>  tools/perf/util/evlist.c | 7 +++++++
>  1 file changed, 7 insertions(+)
>
> Changes since v2:
>
>    * Undo the fact that v2 was accidentally based on v1 instead of
>      perf-tools
>
> Changes since v1:
>
>   * Reduce scope of evsel variable
>   * Add argument label
>   * Change summary to be less specific about the failing test
>   * Add the closes: tag
>
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 95f25e9fb994..979a6053a84d 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -106,6 +106,13 @@ struct evlist *evlist__new_default(void)
>                 evlist = NULL;
>         }
>
> +       if (evlist->core.nr_entries > 1) {

I think you need a NULL check for evlist here.

Thanks,
Namhyung


> +               struct evsel *evsel;
> +
> +               evlist__for_each_entry(evlist, evsel)
> +                       evsel__set_sample_id(evsel, /*can_sample_identifier=*/false);
> +       }
> +
>         return evlist;
>  }
>
> --
> 2.34.1
>