Re: [PATCH v2] perf pmu: Skip test on Arm64 when #slots is zero

[Leo Yan <leo.yan@arm.com>]

On Fri, Apr 10, 2026 at 11:28:23AM +0000, sashiko-bot@kernel.org wrote:

[...]

> > +static bool is_expected_broken_metric(const struct pmu_metric *pm)
> > +{
> > +	if (!strcmp(pm->metric_name, "M1") || !strcmp(pm->metric_name, "M2") ||
> > +	    !strcmp(pm->metric_name, "M3"))
> > +		return true;
> > +
> > +#if defined(__aarch64__)
> > +	/*
> > +	 * Arm64 platforms may return "#slots == 0", which is treated as a
> > +	 * syntax error by the parser. Don't test these metrics when running
> > +	 * on such platforms.
> > +	 */
> > +	if (strstr(pm->metric_expr, "#slots") &&
> > +	    !tool_pmu__cpu_slots_per_cycle())
> 
> Does reading host capabilities via tool_pmu__cpu_slots_per_cycle() bypass
> the fake PMU abstraction used by these tests?
> 
> The fake PMU tests are intended to validate the metric parser across all
> architectures without requiring the actual referenced PMUs or hardware
> capabilities to exist on the host machine.
> 
> Because tool_pmu__cpu_slots_per_cycle() checks the host's
> /sys/bus/event_source/devices/ caps/slots, does this break the test's
> hardware-independent validation?

I agreed that the test is designed for hardware-independent, however,
the low level's parser has already invoked
tool_pmu__cpu_slots_per_cycle() for event parsing, even with the fake
PMU.

[...]

> > @@ -852,8 +873,7 @@ static int test__parsing_callback(const struct pmu_metric *pm,
> >  
> >  	err = metricgroup__parse_groups_test(evlist, table, pm->metric_name);
> >  	if (err) {
> > -		if (!strcmp(pm->metric_name, "M1") || !strcmp(pm->metric_name, "M2") ||
> > -		    !strcmp(pm->metric_name, "M3")) {
> > +		if (is_expected_broken_metric(pm)) {
> >  			(*failures)--;
> >  			pr_debug("Expected broken metric %s skipping\n", pm->metric_name);
> >  			err = 0;
> 
> Does unconditionally clearing the error here create a testing blind spot
> for genuine syntax errors?
> 
> If a metric expression contains "#slots" on an Arm64 host without slot
> support, the failure is ignored entirely. Could this silently hide other
> issues, like typos in other events or malformed operators within the same
> metric expression?

The test will run on PMUs that support #slots, so any malformed metric
expressions can be detected.  Simply say, if a metric is applicable to
a platform, it will be verified on that platform.

I don't think I need any update on this patch.