Re: [PATCH v2] perf evsel: Improve callchain warning for s390

[Jens Remus <jremus@linux.ibm.com>]

On 9/15/2026 9:47 PM, Ian Rogers wrote:
> On Fri, Aug 21, 2026 at 6:03 AM Jens Remus <jremus@linux.ibm.com> wrote:
>>
>> On 8/21/2026 2:55 PM, Jens Remus wrote:
>>
>>> Instead, warn on s390 when callchain sampling is requested with an event
>>> provided by the CPUMSF hardware PMU, because that combination is not
>>> supported.
>>
>>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>>
>>> @@ -1078,9 +1078,8 @@ static void __evsel__config_callchain(struct evsel *evsel, const struct record_o
>>>       bool function = evsel__is_function_event(evsel);
>>>       struct perf_event_attr *attr = &evsel->core.attr;
>>>
>>> -     if (EM_HOST == EM_S390 && param->record_mode == CALLCHAIN_FP) {
>>> -             pr_warning_once(
>>> -                     "Framepointer unwinding lacks kernel support. Use '--call-graph dwarf'\n");
>>> +     if (EM_HOST == EM_S390 && evsel->pmu && !perf_pmu__is_software(evsel->pmu)) {
>>> +             pr_warning_once("Cannot use hardware CPUMSF event with -g and --call-graph.\n");
>>
>> Jan, Thomas, could you please do me a favor and test whether this works
>> as expected on LPAR with CPUMSF?  Time was running out before I leave on
>> vacation.
> 
> Thomas, the change looks good to me. What are your thoughts?

Sent a v3 with updated warning message.

> 
>>>       }
>>>
>>>       evsel__set_sample_bit(evsel, CALLCHAIN);

Regards,
Jens
-- 
Jens Remus
Linux on Z Development (D3303)
jremus@de.ibm.com / jremus@linux.ibm.com

IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Ehningen; Registergericht: Amtsgericht Stuttgart, HRB 243294
IBM Data Privacy Statement: https://www.ibm.com/privacy/