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

[Namhyung Kim <namhyung@kernel.org>]

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