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Date: Wed, 27 May 2020 14:31:03 +0800
From: "Jin, Yao" <yao.jin@...ux.intel.com>
To: Jiri Olsa <jolsa@...hat.com>
Cc: acme@...nel.org, jolsa@...nel.org, peterz@...radead.org,
mingo@...hat.com, alexander.shishkin@...ux.intel.com,
Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
kan.liang@...el.com, yao.jin@...el.com
Subject: Re: [PATCH v2 1/2] perf evlist: Ensure grouped events with same cpu
map
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
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