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

Jin, Yao
2020-05-28T01:47:56Z

Hi Jiri,

On 5/28/2020 12:28 AM, Jiri Olsa wrote:
> On Wed, May 27, 2020 at 09:49:11PM +0800, Jin, Yao wrote:
>> Hi Jiri,
>>
>> On 5/27/2020 6:28 PM, Jiri Olsa wrote:
>>> 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
>>>
>>
>> Let me use this example again.
>>
>> 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,
>>
>> Yes, once for_each_group_member breaks (due to the issue in 'pos->leader =
>> pos'), evlist__for_each_entry will continue to the second
>> unc_cbo_cache_lookup.any_i. But now evsel->leader != evsel (evsel->leader is
>> "cycles"), so it will go to cpu_maps_matched.
>>
>> But actually we don't need to go to cpu_maps_matched again.
>>
>> for_each_group_member(pos, evsel->leader) {
>> pos->leader = pos;
>> pos->core.nr_members = 0;
>> }
>>
>> If we solve the issue in above code, for_each_group_member doesn't break,
>> the leaders of all members in this group will be set to themselves.
>>
>> if (evsel->leader == evsel)
>> continue;
>
> I see.. the problem is in the for_each_group_member, how about
> saving the leader into separate variable, like below
>
> jirka
>
>
> ---
> diff --git a/tools/perf/builtin-stat.c b/tools/perf/builtin-stat.c
> index f789103d8306..a754cad3f5a0 100644
> --- a/tools/perf/builtin-stat.c
> +++ b/tools/perf/builtin-stat.c
> @@ -189,6 +189,51 @@ static struct perf_stat_config stat_config = {
> .big_num = true,
> };
>
> +static bool cpus_map_matched(struct evsel *a, struct evsel *b)
> +{
> + if (!a->core.cpus && !b->core.cpus)
> + return true;
> +
> + if (!a->core.cpus || !b->core.cpus)
> + return false;
> +
> + if (a->core.cpus->nr != b->core.cpus->nr)
> + return false;
> +
> + for (int i = 0; i < a->core.cpus->nr; i++) {
> + if (a->core.cpus->map[i] != b->core.cpus->map[i])
> + return false;
> + }
> +
> + return true;
> +}
> +
> +
> +static void evlist__check_cpu_maps(struct evlist *evlist)
> +{
> + struct evsel *evsel, *pos, *leader;
> +
> + evlist__for_each_entry(evlist, evsel) {
> + char buf[1024];
> +
> + leader = evsel->leader;
> + if (leader == evsel)
> + continue;
> + if (cpus_map_matched(leader, evsel))
> + continue;
> +
> + evsel__group_desc(leader, buf, sizeof(buf));
> + WARN_ONCE(1, "WARNING: event cpu maps do not match, disabling group:\n");
> + pr_warning(" %s\n", buf);
> +
> + for_each_group_evsel(pos, leader) {
> + pos->leader = pos;
> + pos->core.nr_members = 0;
> + }
> + evsel->leader->core.nr_members = 0;
> + }
> +}
> +
> static inline void diff_timespec(struct timespec *r, struct timespec *a,
> struct timespec *b)
> {
> @@ -1956,6 +2001,8 @@ int cmd_stat(int argc, const char **argv)
> } else if (argc && !strncmp(argv[0], "rep", 3))
> return __cmd_report(argc, argv);
>
> + evlist__check_cpu_maps(evsel_list);
> +
> interval = stat_config.interval;
> timeout = stat_config.timeout;
>
>

This patch looks good. I guess you will post this patch, right? Thanks so much! :)

Thanks
Jin Yao