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

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Date: Wed, 24 Jan 2024 09:03:57 +0000
From: James Clark <james.clark@....com>
To: Namhyung Kim <namhyung@...nel.org>
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



On 24/01/2024 00:46, Namhyung Kim wrote:
> 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
> 
> 

Oops yes. Or just return on the error above.

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