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

["Jin, Yao" <yao.jin@linux.intel.com>]

Hi Jiri,

On 5/27/2020 2:31 PM, Jin, Yao wrote:
> Hi Jiri,
> 
> On 5/27/2020 11:20 AM, Jin, Yao wrote:
>> Hi Jiri,
>>
>> On 5/26/2020 7:51 PM, Jiri Olsa wrote:
>>> On Mon, May 25, 2020 at 02:55:58PM +0800, Jin Yao wrote:
>>>
>>> SNIP
>>>
>>>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>>>> index 2a9de6491700..1161cffc0688 100644
>>>> --- a/tools/perf/util/evlist.c
>>>> +++ b/tools/perf/util/evlist.c
>>>> @@ -1704,3 +1704,52 @@ struct evsel *perf_evlist__reset_weak_group(struct evlist *evsel_list,
>>>>       }
>>>>       return leader;
>>>>   }
>>>> +
>>>> +static bool cpus_map_matched(struct evsel *prev, struct evsel *evsel)
>>>> +{
>>>> +    if (evsel->core.cpus->nr != prev->core.cpus->nr)
>>>> +        return false;
>>>> +
>>>> +    for (int i = 0; i < evsel->core.cpus->nr; i++) {
>>>> +        if (evsel->core.cpus->map[i] != prev->core.cpus->map[i])
>>>> +            return false;
>>>> +    }
>>>> +
>>>> +    return true;
>>>> +}
>>>> +
>>>> +bool evlist__cpus_map_matched(struct evlist *evlist)
>>>> +{
>>>> +    struct evsel *prev = evlist__first(evlist), *evsel = prev;
>>>> +    int nr_members = prev->core.nr_members;
>>>> +
>>>> +    evlist__for_each_entry_continue(evlist, evsel) {
>>>> +        if (nr_members <= 1) {
>>>> +            prev = evsel;
>>>> +            nr_members = evsel->core.nr_members;
>>>> +            continue;
>>>> +        }
>>>> +
>>>> +        nr_members--;
>>>> +
>>>> +        if (!cpus_map_matched(prev, evsel))
>>>> +            return false;
>>>> +
>>>> +        prev = evsel;
>>>> +    }
>>>> +
>>>> +    return true;
>>>> +}
>>>> +
>>>> +void evlist__force_disable_group(struct evlist *evlist)
>>>> +{
>>>> +    struct evsel *evsel;
>>>> +
>>>> +    pr_warning("WARNING: event cpu maps are not fully matched, "
>>>> +           "stop event grouping\n");
>>>> +
>>>> +    evlist__for_each_entry(evlist, evsel) {
>>>> +        evsel->leader = evsel;
>>>> +        evsel->core.nr_members = 0;
>>>> +    }
>>>> +}
>>>
>>> I think this is too much, we need to disable only groups with not
>>> matching cpus, not all of them, how about something like this
>>>
>>
>> Yes, that's too much.
>>
>>>
>>>          struct evsel *pos;
>>>
>>>          evlist__for_each_entry(evlist, evsel) {
>>>                  if (evsel->leader == evsel)
>>>                          continue;
>>>                  if (!cpus_map_matched(evsel->leader, evsel))
>>>                          continue;
>>>                  pr_warn("Disabling group...
>>>
>>>                  for_each_group_member(pos, evsel->leader) {
>>>                          pos->leader = pos;
>>>                          evsel->core.nr_members = 0;
>>>                  }
>>>          }
>>>
>>> jirka
>>>
>>
>> Hmm, change "!cpus_map_matched()" to "cpus_map_matched()"? and use for_each_group_evsel() to 
>> replace for_each_group_member()?
>>
>> How about something like following?
>>
>> void evlist__check_cpu_maps(struct evlist *evlist)
>> {
>>      struct evsel *evsel, *pos;
>>
>>      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_evsel(pos, evsel->leader) {
>>              pos->leader = pos;
>>              pos->core.nr_members = 0;
>>          }
>>
>>          /*
>>           * For core & uncore mixed event group, for example,
>>           * '{cycles,unc_cbo_cache_lookup.any_i}',
>>           * 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,
>>           *
>>           * cycles is leader and all unc_cbo_cache_lookup.any_i
>>           * point to this leader. But for_each_group_evsel can't
>>           * iterate all members from cycles. It only iterates
>>           * cycles and one unc_cbo_cache_lookup.any_i. So we
>>           * set extra evsel here.
>>           */
>>          evsel->leader = evsel;
>>          evsel->core.nr_members = 0;
>>      }
>> }
>>
>> 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.
> 
> I'm now thinking if we can solve this issue by an easy way.
> 
> Thanks
> Jin Yao

How about this fix?

void evlist__check_cpu_maps(struct evlist *evlist)
{
	struct evsel *evsel, *pos, *tmp;

	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) {
			if (pos != evsel) {
				pos->leader = pos;
				pos->core.nr_members = 0;
			}
		}

		tmp = evsel->leader;
		tmp->leader = tmp;
		tmp->core.nr_members = 0;

		evsel->leader = evsel;
		evsel->core.nr_members = 0;
	}
}

Thanks
Jin Yao