linux-kernel - Re: [PATCH] perf/x86: Fix open counting event error

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Message-ID: <a04c37c6-8f83-45e9-a39f-1e1ba613f7f4@amd.com>
Date: Fri, 25 Apr 2025 15:42:39 +0530
From: Ravi Bangoria <ravi.bangoria@....com>
To: "Liang, Kan" <kan.liang@...ux.intel.com>
Cc: Luo Gengkun <luogengkun@...weicloud.com>,
 "peterz@...radead.org" <peterz@...radead.org>,
 "mingo@...hat.com" <mingo@...hat.com>, "acme@...nel.org" <acme@...nel.org>,
 "namhyung@...nel.org" <namhyung@...nel.org>,
 "mark.rutland@....com" <mark.rutland@....com>,
 "alexander.shishkin@...ux.intel.com" <alexander.shishkin@...ux.intel.com>,
 "jolsa@...nel.org" <jolsa@...nel.org>,
 "irogers@...gle.com" <irogers@...gle.com>,
 "adrian.hunter@...el.com" <adrian.hunter@...el.com>,
 "tglx@...utronix.de" <tglx@...utronix.de>, "bp@...en8.de" <bp@...en8.de>,
 "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
 "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
 "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Ravi Bangoria <ravi.bangoria@....com>
Subject: Re: [PATCH] perf/x86: Fix open counting event error

Hi Kan,

>>> Perf doesn't work at perf stat for hardware events:
>>>
>>>  $perf stat -- sleep 1
>>>  Performance counter stats for 'sleep 1':
>>>              16.44 msec task-clock                       #    0.016 CPUs utilized
>>>                  2      context-switches                 #  121.691 /sec
>>>                  0      cpu-migrations                   #    0.000 /sec
>>>                 54      page-faults                      #    3.286 K/sec
>>>    <not supported>	cycles
>>>    <not supported>	instructions
>>>    <not supported>	branches
>>>    <not supported>	branch-misses
>>
>> Wondering if it is worth to add this in perf test. Something like
>> below?
>>
>> --- a/tools/perf/tests/shell/stat.sh
>> +++ b/tools/perf/tests/shell/stat.sh
>> @@ -16,6 +16,24 @@ test_default_stat() {
>>    echo "Basic stat command test [Success]"
>>  }
>>  
>> +test_stat_count() {
>> +  echo "stat count test"
>> +
>> +  if ! perf list | grep -q "cpu-cycles OR cycles"
>> +  then
>> +    echo "stat count test [Skipped cpu-cycles event missing]"
>> +    return
>> +  fi
>> +
>> +  if perf stat -e cycles true 2>&1 | grep -E -q "<not supported>"
>> +  then
>> +    echo "stat count test [Failed]"
>> +    err=1
>> +    return
>> +  fi
>> +  echo "stat count test [Success]"
>> +}
>> +
>>  test_stat_record_report() {
>>    echo "stat record and report test"
>>    if ! perf stat record -o - true | perf stat report -i - 2>&1 | \
>> @@ -201,6 +219,7 @@ test_hybrid() {
>>  }
>>  
>>  test_default_stat
>> +test_stat_count
> 
> I think the perf stat default should always be supported, not just cycles.
> Maybe we should add the check in test_default_stat?

Do you mean:

  if perf stat true 2>&1 | grep -E -q "<not supported>"
    err=1

Isn't this ambiguous? Also, this fails on machines where HW pmu
is not supported. For ex, on my qemu guest with `-cpu pmu=off`:

  $ ./perf list | grep "cpu-cycles OR cycles"
  <empty output>

  $ ./perf stat true
   Performance counter stats for 'true':
                0.42 msec task-clock:u                     #    0.470 CPUs utilized
                   0      context-switches:u               #    0.000 /sec
                   0      cpu-migrations:u                 #    0.000 /sec
                  48      page-faults:u                    #  113.874 K/sec
     <not supported>      cycles:u

Thanks,
Ravi