Re: [PATCH v1 1/2] perf evsel: evsel__group_pmu_name fixes

[Adrian Hunter]

On 23/05/23 19:58, Ian Rogers wrote:
> On Tue, May 23, 2023 at 6:01 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>>
>> On 23/05/23 07:44, Ian Rogers wrote:
>>> Previously the evsel__group_pmu_name would iterate the evsel's group,
>>> however, the list of evsels aren't yet sorted and so the loop may
>>> terminate prematurely. It is also not desirable to iterate the list of
>>> evsels during list_sort as the list may be broken. Precompute the
>>> group_pmu_name for the evsel before sorting, as part of the
>>> computation and only if necessary, iterate the whole list looking for
>>> group members so that being sorted isn't necessary.
>>>
>>> Move the group pmu name computation to parse-events.c given the closer
>>> dependency on the behavior of
>>> parse_events__sort_events_and_fix_groups.
>>>
>>> Fixes: 7abf0bccaaec ("perf evsel: Add function to compute group PMU name")
>>> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
>>> ---
>>>  tools/perf/util/evsel.c        | 31 +++++-----------------
>>>  tools/perf/util/evsel.h        |  2 +-
>>>  tools/perf/util/parse-events.c | 47 ++++++++++++++++++++++++++++++----
>>>  3 files changed, 50 insertions(+), 30 deletions(-)
>>>
>>> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
>>> index 2f5910b31fa9..3247773f9e24 100644
>>> --- a/tools/perf/util/evsel.c
>>> +++ b/tools/perf/util/evsel.c
>>> @@ -290,6 +290,7 @@ void evsel__init(struct evsel *evsel,
>>>       evsel->per_pkg_mask  = NULL;
>>>       evsel->collect_stat  = false;
>>>       evsel->pmu_name      = NULL;
>>> +     evsel->group_pmu_name = NULL;
>>>       evsel->skippable     = false;
>>>  }
>>>
>>> @@ -431,6 +432,11 @@ struct evsel *evsel__clone(struct evsel *orig)
>>>               if (evsel->pmu_name == NULL)
>>>                       goto out_err;
>>>       }
>>> +     if (orig->group_pmu_name) {
>>> +             evsel->group_pmu_name = strdup(orig->group_pmu_name);
>>> +             if (evsel->group_pmu_name == NULL)
>>> +                     goto out_err;
>>> +     }
>>>       if (orig->filter) {
>>>               evsel->filter = strdup(orig->filter);
>>>               if (evsel->filter == NULL)
>>> @@ -827,30 +833,6 @@ bool evsel__name_is(struct evsel *evsel, const char *name)
>>>       return !strcmp(evsel__name(evsel), name);
>>>  }
>>>
>>> -const char *evsel__group_pmu_name(const struct evsel *evsel)
>>> -{
>>> -     struct evsel *leader = evsel__leader(evsel);
>>> -     struct evsel *pos;
>>> -
>>> -     /*
>>> -      * Software events may be in a group with other uncore PMU events. Use
>>> -      * the pmu_name of the first non-software event to avoid breaking the
>>> -      * software event out of the group.
>>> -      *
>>> -      * Aux event leaders, like intel_pt, expect a group with events from
>>> -      * other PMUs, so substitute the AUX event's PMU in this case.
>>> -      */
>>> -     if (evsel->core.attr.type == PERF_TYPE_SOFTWARE || evsel__is_aux_event(leader)) {
>>> -             /* Starting with the leader, find the first event with a named PMU. */
>>> -             for_each_group_evsel(pos, leader) {
>>> -                     if (pos->pmu_name)
>>> -                             return pos->pmu_name;
>>> -             }
>>> -     }
>>> -
>>> -     return evsel->pmu_name ?: "cpu";
>>> -}
>>> -
>>>  const char *evsel__metric_id(const struct evsel *evsel)
>>>  {
>>>       if (evsel->metric_id)
>>> @@ -1536,6 +1518,7 @@ void evsel__exit(struct evsel *evsel)
>>>       zfree(&evsel->group_name);
>>>       zfree(&evsel->name);
>>>       zfree(&evsel->pmu_name);
>>> +     zfree(&evsel->group_pmu_name);
>>>       zfree(&evsel->unit);
>>>       zfree(&evsel->metric_id);
>>>       evsel__zero_per_pkg(evsel);
>>> diff --git a/tools/perf/util/evsel.h b/tools/perf/util/evsel.h
>>> index df8928745fc6..820771a649b2 100644
>>> --- a/tools/perf/util/evsel.h
>>> +++ b/tools/perf/util/evsel.h
>>> @@ -72,6 +72,7 @@ struct evsel {
>>>               char                    *name;
>>>               char                    *group_name;
>>>               const char              *pmu_name;
>>> +             const char              *group_pmu_name;
>>
>> Since it seems to be only used when sorting, do we really
>> need this on struct evsel?
> 
> Agreed. There is also redundancy between evsel->pmu_name and
> evsel->pmu->name. For now having it here makes the coding easier and
> it could be a useful were we to do more with sorting, like sorting the
> final evlist rather than each evlist post parsing, or for debug
> output.
> 
>>>  #ifdef HAVE_LIBTRACEEVENT
>>>               struct tep_event        *tp_format;
>>>  #endif
>>> @@ -289,7 +290,6 @@ int arch_evsel__hw_name(struct evsel *evsel, char *bf, size_t size);
>>>  int __evsel__hw_cache_type_op_res_name(u8 type, u8 op, u8 result, char *bf, size_t size);
>>>  const char *evsel__name(struct evsel *evsel);
>>>  bool evsel__name_is(struct evsel *evsel, const char *name);
>>> -const char *evsel__group_pmu_name(const struct evsel *evsel);
>>>  const char *evsel__metric_id(const struct evsel *evsel);
>>>
>>>  static inline bool evsel__is_tool(const struct evsel *evsel)
>>> diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
>>> index 34ba840ae19a..210e6f713c6f 100644
>>> --- a/tools/perf/util/parse-events.c
>>> +++ b/tools/perf/util/parse-events.c
>>> @@ -2125,6 +2125,41 @@ static int parse_events__with_hybrid_pmu(struct parse_events_state *parse_state,
>>>       return ret;
>>>  }
>>>
>>> +static void evsel__compute_group_pmu_name(struct evsel *evsel,
>>> +                                       const struct list_head *head)
>>> +{
>>> +     struct evsel *leader = evsel__leader(evsel);
>>> +     struct evsel *pos;
>>> +
>>> +     /*
>>> +      * Software events may be in a group with other uncore PMU events. Use
>>> +      * the pmu_name of the first non-software event to avoid breaking the
>>> +      * software event out of the group.
>>> +      *
>>> +      * Aux event leaders, like intel_pt, expect a group with events from
>>> +      * other PMUs, so substitute the AUX event's PMU in this case.
>>> +      */
>>> +     if (evsel->core.attr.type == PERF_TYPE_SOFTWARE || evsel__is_aux_event(leader)) {
>>> +             /*
>>> +              * Starting with the leader, find the first event with a named
>>> +              * PMU. for_each_group_(member|evsel) isn't used as the list
>>> +              * isn't yet sorted putting evsel's in the same group together.
>>> +              */
>>> +             if (leader->pmu_name) {
>>> +                     evsel->group_pmu_name = strdup(leader->pmu_name);
>>> +                     return;
>>> +             }
>>> +             list_for_each_entry(pos, head, core.node) {
>>> +                     if (evsel__leader(pos) == leader && pos->pmu_name) {
>>> +                             evsel->group_pmu_name = strdup(pos->pmu_name);
>>> +                             return;
>>> +                     }
>>> +             }
>>> +     }
>>> +
>>> +     evsel->group_pmu_name = strdup(evsel->pmu_name ?: "cpu");
>>> +}
>>> +
>>>  __weak int arch_evlist__cmp(const struct evsel *lhs, const struct evsel *rhs)
>>>  {
>>>       /* Order by insertion index. */
>>> @@ -2160,8 +2195,8 @@ static int evlist__cmp(void *state, const struct list_head *l, const struct list
>>>
>>>       /* Group by PMU if there is a group. Groups can't span PMUs. */
>>>       if (lhs_has_group && rhs_has_group) {
>>> -             lhs_pmu_name = evsel__group_pmu_name(lhs);
>>> -             rhs_pmu_name = evsel__group_pmu_name(rhs);
>>> +             lhs_pmu_name = lhs->group_pmu_name;
>>> +             rhs_pmu_name = rhs->group_pmu_name;
>>>               ret = strcmp(lhs_pmu_name, rhs_pmu_name);
>>>               if (ret)
>>>                       return ret;
>>> @@ -2186,6 +2221,8 @@ static bool parse_events__sort_events_and_fix_groups(struct list_head *list)
>>>       list_for_each_entry(pos, list, core.node) {
>>>               const struct evsel *pos_leader = evsel__leader(pos);
>>>
>>> +             evsel__compute_group_pmu_name(pos, list);
>>
>> Perhaps check for failing to allocate the string?
> 
> Will fix in v2.
> 
>> But alternatively, allocate an array for pointers to the
>> group pmu names.  Then they don't needed to be strdup'ed,
>> or stored on evsel.  Would have to count the number of evsel
>> first though.
>>
>>         group_pmu_names = calloc(nr_evsel, sizeof(const char *));
>>
>>         group_pmu_names[pos->core.idx] = evsel__group_pmu_name(pos);
> 
> Possibly, I'd prefer to keep it as simple as possible until we think
> we should optimize.
> 
>>> +
>>>               if (pos == pos_leader)
>>>                       orig_num_leaders++;
>>>
>>> @@ -2210,7 +2247,7 @@ static bool parse_events__sort_events_and_fix_groups(struct list_head *list)
>>>       idx = 0;
>>>       list_for_each_entry(pos, list, core.node) {
>>>               const struct evsel *pos_leader = evsel__leader(pos);
>>> -             const char *pos_pmu_name = evsel__group_pmu_name(pos);
>>> +             const char *pos_pmu_name = pos->group_pmu_name;
>>>               const char *cur_leader_pmu_name, *pos_leader_pmu_name;
>>>               bool force_grouped = arch_evsel__must_be_in_group(pos);
>>>
>>> @@ -2227,7 +2264,7 @@ static bool parse_events__sort_events_and_fix_groups(struct list_head *list)
>>>               if (!cur_leader)
>>>                       cur_leader = pos;
>>>
>>> -             cur_leader_pmu_name = evsel__group_pmu_name(cur_leader);
>>> +             cur_leader_pmu_name = cur_leader->group_pmu_name;
>>>               if ((cur_leaders_grp != pos->core.leader && !force_grouped) ||
>>>                   strcmp(cur_leader_pmu_name, pos_pmu_name)) {
>>>                       /* Event is for a different group/PMU than last. */
>>> @@ -2239,7 +2276,7 @@ static bool parse_events__sort_events_and_fix_groups(struct list_head *list)
>>>                        */
>>>                       cur_leaders_grp = pos->core.leader;
>>>               }
>>> -             pos_leader_pmu_name = evsel__group_pmu_name(pos_leader);
>>> +             pos_leader_pmu_name = pos_leader->group_pmu_name;
>>>               if (strcmp(pos_leader_pmu_name, pos_pmu_name) || force_grouped) {
>>>                       /*
>>>                        * Event's PMU differs from its leader's. Groups can't
>>
>> By the way, do we really need unsorted_idx?
> 
> Right, I've played around with this a bit. I'll have a go at
> explaining the motivation below.
> 
>> For example what about this for evlist__cmp():
>>
>> static int evlist__cmp(void *state __maybe_unused, const struct list_head *l, const struct list_head *r)
>> {
>>         const struct evsel *lhs = container_of(l, struct evsel, core.node);
>>         const struct evsel *rhs = container_of(r, struct evsel, core.node);
>>         int lhs_leader_idx = lhs->core.leader->idx;
>>         int rhs_leader_idx = rhs->core.leader->idx;
>>         int ret;
>>
>>         if (lhs_leader_idx != rhs_leader_idx)
>>                 return lhs_leader_idx - rhs_leader_idx;
> 
> So here any ungrouped evsels, or evsels in different groups will cause
> evlist__cmp to terminate.
> 
>>         ret = strcmp(evsel__group_pmu_name(lhs), evsel__group_pmu_name(rhs));
>>         if (ret)
>>                 return ret;
> 
> This is redundant as the leader matches on both lhs and rhs given the
> test above.
> 
>>         /* Architecture specific sorting. */
>>         return arch_evlist__cmp(lhs, rhs);
> 
> We'll never reach here for cases like ungrouped topdown (perf metric)
> events where we want to sort the topdown events to allow grouping. I
> think the comment:
> 
> /*
> * First sort by grouping/leader. Read the leader idx only if the evsel
> * is part of a group, as -1 indicates no group.
> */
> 
> isn't clear. I'll tweak it in v2, I think it would be better as something like:
> 
> /*
> * First sort by grouping/leader. Read the leader idx only if the evsel
> * is part of a group, by default ungrouped events will be sorted relative
> * to grouped events based
> * on where the first ungrouped event occurs. If both events don't have
> * a group we want to fall-through to the arch specific sorting, that can
> * reorder and fix things like Intel's topdown events.
> */
> 
> To go back to why the code became this way. By default we'll place
> metric's events into a weak group and if the perf_event_open fails
> we'll break the group. We're smart enough to know when breaking a
> group of events that the topdown event's group must not be broken.
> However, there are cases where the perf_event_open succeeds but then
> the counters yield "<not counted>" as they are part of a group. I've
> asked for kernel fixes to fail the perf_event_open, maybe they'll
> happen, for now I need to be able to work on old kernels anyway.
> Metrics with "<not counted>" events are now tagged as saying the
> events shouldn't be grouped but this has a problem of breaking the
> grouping for topdown events. We already had to sort events for cases
> like "{imc/cas_count_read/,imc/cas_count_write/}" where we have
> multiple imc PMUs and we need to group cas_count_read and
> cas_count_write events for each PMU - the eventual grouping looks like
> "{uncore_imc_0/cas_count_read/,uncore_imc_0/cas_count_write/},{uncore_imc_1/cas_count_read/,uncore_imc_1/cas_count_write/}...".
> The aim with the code was to have a single sorting mechanism for the
> existing uncore case and the new ungrouped topdown events case.

Are there any tests for that?