Re: [PATCH] perf test: Fix test case 120 and 121 for s390

Thomas Richter
2026-03-11T07:21:59Z

On 3/11/26 07:09, Namhyung Kim wrote:
> On Mon, Mar 09, 2026 at 11:18:28AM -0700, Ian Rogers wrote:
>> On Mon, Mar 9, 2026 at 5:59 AM Thomas Richter <tmricht@linux.ibm.com> wrote:
>>>
>>> On 3/6/26 17:53, Ian Rogers wrote:
>>>> On Fri, Mar 6, 2026 at 7:52 AM Jan Polensky <japo@linux.ibm.com> wrote:
>>>>>
>>>>> On Fri, Mar 06, 2026 at 08:10:02AM +0100, Thomas Richter wrote:
>>>>>> Perf tests
>>>>>> 120: 'perf data convert --to-ctf' command test
>>>>>> 121: 'perf data convert --to-json' command test
>>>>>> fail on s390. It is caused by selecting the default event cycles
>>>>>> which does not exist on s390 z/VM. Use software event cpu-clock
>>>>>> and specify it explicitly on the command line.
>>>>>>
>>>>>> Output before:
>>>>>> ❯ perf test 120 121
>>>>>> 120: 'perf data convert --to-ctf' command test : FAILED!
>>>>>> 121: 'perf data convert --to-json' command test : FAILED!
>>>>>>
>>>>>> Output after:
>>>>>> ❯ perf test 120 121
>>>>>> 120: 'perf data convert --to-ctf' command test : Ok
>>>>>> 121: 'perf data convert --to-json' command test : Ok
>>>>>>
>>>>>> Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
>>>>> [snip]
>>>>> Thanks for providing this, Thomas!
>>>>> Tested-by: Jan Polensky <japo@linux.ibm.com>
>>>>> Reviewed-by: Jan Polensky <japo@linux.ibm.com>
>>>>
>>>> Should we not fallback for the cycles as a default event?
>>>> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/builtin-record.c#n1374
>>>> https://web.git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/perf/util/evsel.c#n3792
>>>>
>>>> Thanks,
>>>> Ian
>>>>
>>>
>>> The fallback should be cpu-clock in case hardware event cycles (or CPU_CYCLES on s390) does not exist.
>>
>> Thanks Thomas, so the change is doing:
>> ```
>> - if ! perf record -o "$perfdata" -F 99 -g -- perf test -w noploop
>> + if ! perf record -o "$perfdata" -e cpu-clock -F 99 -g -- perf
>> test -w noploop
>> ```
>> where the default event is cycles:
>> https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/util/evlist.c#n116
>> Given that cycles will fail but then fallback to cpu-clock:
>> https://web.git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf/util/evsel.c#n3792
>> I wonder if the issue is that the fallback is broken. Specifically:
>> ```
>> evsel->core.attr.type == PERF_TYPE_HARDWARE &&
>> evsel->core.attr.config == PERF_COUNT_HW_CPU_CYCLES) {
>> ```
>> It isn't going to work well on hybrid machines or those whose PMU's
>> sysfs events or JSON include a cycles event. I wonder if using
>> `evsel__match(evsel, HARDWARE, CYCLES)` would be better, as the
>> evsel__match code is more robust to these kind of variances. I don't
>> know if that will address the fallback problem for you.
>
> I suspect it may return a different error code on s390.
>
> Thanks,
> Namhyung
>

This is interesting, further debugging revealed this:
# ./perf record -F 99 --call-graph dwarf -F99 -- perf test -w noploop
Error:
Failure to open event 'cpum_cf/cycles/PH' on PMU 'cpum_cf' which will be removed.
cpum_cf/cycles/PH: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'
Error:
Failure to open any events for recording.
# ./perf record -F 99 -g -- perf test -w noploop
Error:
Failure to open event 'cpum_cf/cycles/PH' on PMU 'cpum_cf' which will be removed.
cpum_cf/cycles/PH: PMU Hardware doesn't support sampling/overflow-interrupts. Try 'perf stat'
Error:
Failure to open any events for recording.
# ./perf record -F 99 -- perf test -w noploop
[ perf record: Woken up 1 times to write data ]
Failed to open /proc/schedstat
[ perf record: Captured and wrote 0.012 MB perf.data (95 samples) ]
#

So the real issue is the -g / --call-graph dwarf option. s390 supports only dwarf.
But with --call-graph event 'cpum_cf/cycles/PH' is used, that is modifier H is added.
# ./perf evlist
cpum_cf/cycles/P
#

Without that option modifier H is not added and all is well.

I suggest to drop the call-graph option. If that option is needed for the test
than we need a s390 change anyway.

--
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

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