linux-kernel - Re: [PATCH v3 3/7] perf evsel: Add iterator to iterate over events ordered by CPU

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Date:   Wed, 30 Oct 2019 08:51:08 -0700
From:   Andi Kleen <andi@...stfloor.org>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Andi Kleen <andi@...stfloor.org>, acme@...nel.org,
        jolsa@...nel.org, eranian@...gle.com, linux-kernel@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v3 3/7] perf evsel: Add iterator to iterate over events
 ordered by CPU

On Wed, Oct 30, 2019 at 11:06:06AM +0100, Jiri Olsa wrote:
> > +struct perf_cpu_map *evlist__cpu_iter_start(struct evlist *evlist)
> > +{
> > +	struct perf_cpu_map *cpus;
> > +	struct evsel *pos;
> > +
> > +	/*
> > +	 * evlist->cpus is not necessarily a superset of all the
> > +	 * event's cpus, so compute our own super set. This
> > +	 * assume that there is a super set
> > +	 */
> > +	cpus = evlist->core.cpus;
> > +	evlist__for_each_entry(evlist, pos) {
> > +		pos->cpu_index = 0;
> > +		if (pos->core.cpus->nr > cpus->nr)
> > +			cpus = pos->core.cpus;
> > +	}
> > +	return cpus;
> 
> I might not understand the reason for cpu_index, but 

This is just so that we can iterate each event's map
independently.

> imagine something like below should be enough, no?

Well it's more complicated because evlist->all_cpus doesn't exist.
The exists evlist->cpus cannot be used (I tried that)
I also don't think we have an existing function to merge
two maps, so that would need to be added to create it.
Just using ->cpu_index is a much simpler change.


-Andi