linux-kernel - Re: [PATCH 2/2 v3] perf test: Change event in perf test 114 perf record test subtest test_leader

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Message-ID: <d041a9b4-3948-4aa0-985c-632b2eb9b64c@linux.intel.com>
Date: Fri, 7 Feb 2025 10:15:32 +0800
From: "Mi, Dapeng" <dapeng1.mi@...ux.intel.com>
To: "Liang, Kan" <kan.liang@...ux.intel.com>,
 Namhyung Kim <namhyung@...nel.org>, Thomas Richter <tmricht@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
 acme@...nel.org, linux-s390@...r.kernel.org, james.clark@...aro.org,
 agordeev@...ux.ibm.com, gor@...ux.ibm.com, sumanthk@...ux.ibm.com,
 hca@...ux.ibm.com
Subject: Re: [PATCH 2/2 v3] perf test: Change event in perf test 114 perf
 record test subtest test_leader_sampling


On 2/6/2025 10:25 PM, Liang, Kan wrote:
>
> On 2025-02-06 12:42 a.m., Mi, Dapeng wrote:
>> On 2/4/2025 11:55 PM, Liang, Kan wrote:
>>> On 2025-02-03 10:42 p.m., Namhyung Kim wrote:
>>>> Add Kan and Dapeng to CC.
>>>>
>>>> Thanks,
>>>> Namhyung
>>>>
>>>>
>>>> On Fri, Jan 31, 2025 at 11:27:56AM +0100, Thomas Richter wrote:
>>>>> On s390 the event instructions can not be used for recording.
>>>>> This event is only supported by perf stat.
>>>>>
>>>>> Change the event from instructions to cycles in
>>>>> subtest test_leader_sampling.
>>>>>
>>>>> Signed-off-by: Thomas Richter <tmricht@...ux.ibm.com>
>>>>> Suggested-by: James Clark <james.clark@...aro.org>
>>>>> Reviewed-by: James Clark <james.clark@...aro.org>
>>>>> ---
>>>>>  tools/perf/tests/shell/record.sh | 10 +++++-----
>>>>>  1 file changed, 5 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/tools/perf/tests/shell/record.sh b/tools/perf/tests/shell/record.sh
>>>>> index fe2d05bcbb1f..ba8d873d3ca7 100755
>>>>> --- a/tools/perf/tests/shell/record.sh
>>>>> +++ b/tools/perf/tests/shell/record.sh
>>>>> @@ -231,7 +231,7 @@ test_cgroup() {
>>>>>  
>>>>>  test_leader_sampling() {
>>>>>    echo "Basic leader sampling test"
>>>>> -  if ! perf record -o "${perfdata}" -e "{instructions,instructions}:Su" -- \
>>>>> +  if ! perf record -o "${perfdata}" -e "{cycles,cycles}:Su" -- \
>>>>>      perf test -w brstack 2> /dev/null
>>> As a non-precise test, using cycles instead should be fine. But we
>>> should never use it for precise test, e.g., with p. Because cycles is a
>>> non-precise event. It would not surprise me if there is a skid when
>>> reading two cycles events at the point when the event overflow occurs.
>>>
>>> Reviewed-by: Kan Liang <kan.liang@...ux.intel.com>
>> Kan, I suppose you mean only the case without counter snapshot, right? With
>> counter snapshot's help, there would be same period even for non-precise
>> events, right?
> No, the counter-snapshot doesn't help. That's why I suggested to not
> utilize it via enabling the modifier p. It should work for most of the
> cases. But it's not 100% guaranteed for some non-precise events that the
> same period is got at overflow. Since it's a test that could be run
> everywhere, the occasional false alarm would just bring troubles.
>
> Without p, it falls back to the traditional way of handling the sampling
> read. In the PMI handler, the global control is disabled first, then all
> the counters are read. The value may not be very accurate, since it's
> stopped at the PMI handler, not the counter overflow. But because of the
> global control, all the counters stop at the same time. The skid would
> be the same. The test should work.

Got it. Thanks for explaining.


>
> Thanks,
> Kan
>>
>>> Thanks,
>>> Kan
>>>
>>>>>    then
>>>>>      echo "Leader sampling [Failed record]"
>>>>> @@ -243,15 +243,15 @@ test_leader_sampling() {
>>>>>    while IFS= read -r line
>>>>>    do
>>>>>      # Check if the two instruction counts are equal in each record
>>>>> -    instructions=$(echo $line | awk '{for(i=1;i<=NF;i++) if($i=="instructions:") print $(i-1)}')
>>>>> -    if [ $(($index%2)) -ne 0 ] && [ ${instructions}x != ${prev_instructions}x ]
>>>>> +    cycles=$(echo $line | awk '{for(i=1;i<=NF;i++) if($i=="cycles:") print $(i-1)}')
>>>>> +    if [ $(($index%2)) -ne 0 ] && [ ${cycles}x != ${prev_cycles}x ]
>>>>>      then
>>>>> -      echo "Leader sampling [Failed inconsistent instructions count]"
>>>>> +      echo "Leader sampling [Failed inconsistent cycles count]"
>>>>>        err=1
>>>>>        return
>>>>>      fi
>>>>>      index=$(($index+1))
>>>>> -    prev_instructions=$instructions
>>>>> +    prev_cycles=$cycles
>>>>>    done < $script_output
>>>>>    echo "Basic leader sampling test [Success]"
>>>>>  }
>>>>> -- 
>>>>> 2.48.1
>> The code changes look good for me.
>>
>>