Re: [PATCH v2 1/2] perf evlist: Ensure grouped events with same cpu map

Jiri Olsa
2020-05-27T10:28:18Z

On Wed, May 27, 2020 at 02:31:03PM +0800, Jin, Yao wrote:

SNIP

> > Thanks
> > Jin Yao
>
> Issue is found!
>
> It looks we can't set "pos->leader = pos" in either for_each_group_member()
> or in for_each_group_evsel() because it may exit the iteration immediately.
>
> evlist__for_each_entry(evlist, evsel) {
> if (evsel->leader == evsel)
> continue;
>
> if (cpu_maps_matched(evsel->leader, evsel))
> continue;
>
> pr_warning("WARNING: event cpu maps are not fully matched, "
> "disable group\n");
>
> for_each_group_member(pos, evsel->leader) {
> pos->leader = pos;
> pos->core.nr_members = 0;
> }
>
> Let me use the example of '{cycles,unc_cbo_cache_lookup.any_i}' again.
>
> In evlist:
> cycles,
> unc_cbo_cache_lookup.any_i,
> unc_cbo_cache_lookup.any_i,
> unc_cbo_cache_lookup.any_i,
> unc_cbo_cache_lookup.any_i,
>
> When we reach the for_each_group_member at first time, evsel is the first
> unc_cbo_cache_lookup.any_i and evsel->leader is cycles. pos is same as the
> evsel (the first unc_cbo_cache_lookup.any_i).
>
> Once we execute "pos->leader = pos;", it's actually "evsel->leader = evsel".
> So now evsel->leader is changed to the first unc_cbo_cache_lookup.any_i.
>
> In next iteration, pos is the second unc_cbo_cache_lookup.any_i. pos->leader
> is cycles but unfortunately evsel->leader has been changed to the first
> unc_cbo_cache_lookup.any_i. So iteration stops immediately.

hum, AFAICS the iteration will not break but continue to next evsel and
pass the 'continue' for another group member.. what do I miss?

jirka

>
> I'm now thinking if we can solve this issue by an easy way.
>
> Thanks
> Jin Yao
>