Re: [PATCH] perf pmu: Fix event list for uncore PMUs

[John Garry]

On 21/12/2021 09:35, Jiri Olsa wrote:
> On Tue, Dec 21, 2021 at 09:10:37AM +0000, John Garry wrote:
> > On 21/12/2021 07:58, Jiri Olsa wrote:
> > > > +	/* Different names -> never duplicates */
> > > > +	if (strcmp(alias_a->name, alias_b->name))
> > > > +		return false;
> > > > +	if (!alias_a->pmu)
> > > > +		return true;
> > > > +	if (!alias_b->pmu)
> > > > +		return true;
> > > nit could be:
> > >
> > > 	if (!alias_a->pmu || !alias_b->pmu)
> > > 		return true;
> > >
> > > would be great to have more comments explaining the check
> >
> > This is just a sanity check that both strings are non-NULL as we do a
> > strcmp() next. So would this be better:
> >
> > if (!alias_a->pmu || !alias_b->pmu || !strcmp(alias_a->pmu, alias_b->pmu))
> > 	return true
> >
> > ?
> >
> > It will spill a line.
>
> sure, it cought my eye because the is_cpu check later is done on
> the same line, so I started wondering what's the difference ;-)

Now thinking a bit more I am not confident that this patch is a full fix.

arm have heterogeneous CPU systems as well - which are not "hybrid" - 
and I need to ensure that aliasing is still working properly there, as I 
think that this following check would stop removing duplicates there:

+	/* uncore PMUs */
+	if (!alias_a->is_cpu && !alias_b->is_cpu)
+		return true;
+	return false;

Thanks,
John