[v2,2/7] perf evlist: Add evlist__findnew_tracking_event() helper

  Currently, intel-bts, intel-pt, and arm-spe may add a dummy event for
tracking to the evlist. We may need to search for the dummy event for
some settings. Therefore, add evlist__findnew_tracking_event() helper.

evlist__findnew_tracking_event() also deal with system_wide maps if
system_wide is true.

Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
---
 tools/perf/builtin-record.c | 11 +++--------
 tools/perf/util/evlist.c    | 18 ++++++++++++++++++
 tools/perf/util/evlist.h    |  1 +
 3 files changed, 22 insertions(+), 8 deletions(-)
  

On Fri, Jul 14, 2023 at 8:31 PM Yang Jihong <yangjihong1@huawei.com> wrote:
>
> Currently, intel-bts, intel-pt, and arm-spe may add a dummy event for
> tracking to the evlist. We may need to search for the dummy event for
> some settings. Therefore, add evlist__findnew_tracking_event() helper.
>
> evlist__findnew_tracking_event() also deal with system_wide maps if
> system_wide is true.

I'm wondering if we can simplify the naming in the API, we have "dummy
event" which makes sense as we literally call the event "dummy",
"sideband" which refers to the kind of samples/events the dummy event
will record but "tracking" I think tends to get used as a verb rather
than a noun. So I think evlist__findnew_tracking_event should be
evlist__findnew_dummy_event.

Thanks,
Ian

> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
> ---
>  tools/perf/builtin-record.c | 11 +++--------
>  tools/perf/util/evlist.c    | 18 ++++++++++++++++++
>  tools/perf/util/evlist.h    |  1 +
>  3 files changed, 22 insertions(+), 8 deletions(-)
>
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index aec18db7ff23..ca83599cc50c 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -1295,14 +1295,9 @@ static int record__open(struct record *rec)
>          */
>         if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
>             perf_pmus__num_core_pmus() > 1) {
> -               pos = evlist__get_tracking_event(evlist);
> -               if (!evsel__is_dummy_event(pos)) {
> -                       /* Set up dummy event. */
> -                       if (evlist__add_dummy(evlist))
> -                               return -ENOMEM;
> -                       pos = evlist__last(evlist);
> -                       evlist__set_tracking_event(evlist, pos);
> -               }
> +               pos = evlist__findnew_tracking_event(evlist, false);
> +               if (!pos)
> +                       return -ENOMEM;
>
>                 /*
>                  * Enable the dummy event when the process is forked for
> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> index 7ef43f72098e..25c3ebe2c2f5 100644
> --- a/tools/perf/util/evlist.c
> +++ b/tools/perf/util/evlist.c
> @@ -1694,6 +1694,24 @@ void evlist__set_tracking_event(struct evlist *evlist, struct evsel *tracking_ev
>         tracking_evsel->tracking = true;
>  }
>
> +struct evsel *evlist__findnew_tracking_event(struct evlist *evlist, bool system_wide)
> +{
> +       struct evsel *evsel;
> +
> +       evsel = evlist__get_tracking_event(evlist);
> +       if (!evsel__is_dummy_event(evsel)) {
> +               evsel = evlist__add_aux_dummy(evlist, system_wide);
> +               if (!evsel)
> +                       return NULL;
> +
> +               evlist__set_tracking_event(evlist, evsel);
> +       } else if (system_wide) {
> +               perf_evlist__go_system_wide(&evlist->core, &evsel->core);
> +       }
> +
> +       return evsel;
> +}
> +
>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str)
>  {
>         struct evsel *evsel;
> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> index 664c6bf7b3e0..98e7ddb2bd30 100644
> --- a/tools/perf/util/evlist.h
> +++ b/tools/perf/util/evlist.h
> @@ -387,6 +387,7 @@ bool evlist_cpu_iterator__end(const struct evlist_cpu_iterator *evlist_cpu_itr);
>
>  struct evsel *evlist__get_tracking_event(struct evlist *evlist);
>  void evlist__set_tracking_event(struct evlist *evlist, struct evsel *tracking_evsel);
> +struct evsel *evlist__findnew_tracking_event(struct evlist *evlist, bool system_wide);
>
>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str);
>
> --
> 2.30.GIT
>
  

On 19/07/23 19:44, Ian Rogers wrote:
> On Fri, Jul 14, 2023 at 8:31 PM Yang Jihong <yangjihong1@huawei.com> wrote:
>>
>> Currently, intel-bts, intel-pt, and arm-spe may add a dummy event for
>> tracking to the evlist. We may need to search for the dummy event for
>> some settings. Therefore, add evlist__findnew_tracking_event() helper.
>>
>> evlist__findnew_tracking_event() also deal with system_wide maps if
>> system_wide is true.
> 
> I'm wondering if we can simplify the naming in the API, we have "dummy
> event" which makes sense as we literally call the event "dummy",
> "sideband" which refers to the kind of samples/events the dummy event
> will record but "tracking" I think tends to get used as a verb rather
> than a noun. So I think evlist__findnew_tracking_event should be
> evlist__findnew_dummy_event.

Except the tracking event has "tracking" set but there can be other dummy
events that do not.

> 
> Thanks,
> Ian
> 
>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
>> ---
>>  tools/perf/builtin-record.c | 11 +++--------
>>  tools/perf/util/evlist.c    | 18 ++++++++++++++++++
>>  tools/perf/util/evlist.h    |  1 +
>>  3 files changed, 22 insertions(+), 8 deletions(-)
>>
>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>> index aec18db7ff23..ca83599cc50c 100644
>> --- a/tools/perf/builtin-record.c
>> +++ b/tools/perf/builtin-record.c
>> @@ -1295,14 +1295,9 @@ static int record__open(struct record *rec)
>>          */
>>         if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
>>             perf_pmus__num_core_pmus() > 1) {
>> -               pos = evlist__get_tracking_event(evlist);
>> -               if (!evsel__is_dummy_event(pos)) {
>> -                       /* Set up dummy event. */
>> -                       if (evlist__add_dummy(evlist))
>> -                               return -ENOMEM;
>> -                       pos = evlist__last(evlist);
>> -                       evlist__set_tracking_event(evlist, pos);
>> -               }
>> +               pos = evlist__findnew_tracking_event(evlist, false);
>> +               if (!pos)
>> +                       return -ENOMEM;
>>
>>                 /*
>>                  * Enable the dummy event when the process is forked for
>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>> index 7ef43f72098e..25c3ebe2c2f5 100644
>> --- a/tools/perf/util/evlist.c
>> +++ b/tools/perf/util/evlist.c
>> @@ -1694,6 +1694,24 @@ void evlist__set_tracking_event(struct evlist *evlist, struct evsel *tracking_ev
>>         tracking_evsel->tracking = true;
>>  }
>>
>> +struct evsel *evlist__findnew_tracking_event(struct evlist *evlist, bool system_wide)
>> +{
>> +       struct evsel *evsel;
>> +
>> +       evsel = evlist__get_tracking_event(evlist);
>> +       if (!evsel__is_dummy_event(evsel)) {
>> +               evsel = evlist__add_aux_dummy(evlist, system_wide);
>> +               if (!evsel)
>> +                       return NULL;
>> +
>> +               evlist__set_tracking_event(evlist, evsel);
>> +       } else if (system_wide) {
>> +               perf_evlist__go_system_wide(&evlist->core, &evsel->core);
>> +       }
>> +
>> +       return evsel;
>> +}
>> +
>>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str)
>>  {
>>         struct evsel *evsel;
>> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
>> index 664c6bf7b3e0..98e7ddb2bd30 100644
>> --- a/tools/perf/util/evlist.h
>> +++ b/tools/perf/util/evlist.h
>> @@ -387,6 +387,7 @@ bool evlist_cpu_iterator__end(const struct evlist_cpu_iterator *evlist_cpu_itr);
>>
>>  struct evsel *evlist__get_tracking_event(struct evlist *evlist);
>>  void evlist__set_tracking_event(struct evlist *evlist, struct evsel *tracking_evsel);
>> +struct evsel *evlist__findnew_tracking_event(struct evlist *evlist, bool system_wide);
>>
>>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str);
>>
>> --
>> 2.30.GIT
>>
  

On Wed, Jul 19, 2023 at 9:59 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>
> On 19/07/23 19:44, Ian Rogers wrote:
> > On Fri, Jul 14, 2023 at 8:31 PM Yang Jihong <yangjihong1@huawei.com> wrote:
> >>
> >> Currently, intel-bts, intel-pt, and arm-spe may add a dummy event for
> >> tracking to the evlist. We may need to search for the dummy event for
> >> some settings. Therefore, add evlist__findnew_tracking_event() helper.
> >>
> >> evlist__findnew_tracking_event() also deal with system_wide maps if
> >> system_wide is true.
> >
> > I'm wondering if we can simplify the naming in the API, we have "dummy
> > event" which makes sense as we literally call the event "dummy",
> > "sideband" which refers to the kind of samples/events the dummy event
> > will record but "tracking" I think tends to get used as a verb rather
> > than a noun. So I think evlist__findnew_tracking_event should be
> > evlist__findnew_dummy_event.
>
> Except the tracking event has "tracking" set but there can be other dummy
> events that do not.

Thanks! I'm wondering what a dummy event without tracking would be
used for - do you have a reference? I don't see anything in
perf_event.h calling things like mmap2/comm in perf_event_attr
tracking. I'm not a fan of dummy due to it not being intention
revealing. Perhaps if we could go back in time  we could call the
event "sideband", maybe we should migrate to this. We have other
non-obvious uses of the term dummy like in cpumap:
https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/lib/perf/include/perf/cpumap.h?h=perf-tools-next#n24
If tracking can be on any event then does that make the functions
behavior more ambiguous if it means dummy+tracking not <any
event>+tracking?

Thanks,
Ian

> >
> > Thanks,
> > Ian
> >
> >> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
> >> ---
> >>  tools/perf/builtin-record.c | 11 +++--------
> >>  tools/perf/util/evlist.c    | 18 ++++++++++++++++++
> >>  tools/perf/util/evlist.h    |  1 +
> >>  3 files changed, 22 insertions(+), 8 deletions(-)
> >>
> >> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> >> index aec18db7ff23..ca83599cc50c 100644
> >> --- a/tools/perf/builtin-record.c
> >> +++ b/tools/perf/builtin-record.c
> >> @@ -1295,14 +1295,9 @@ static int record__open(struct record *rec)
> >>          */
> >>         if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
> >>             perf_pmus__num_core_pmus() > 1) {
> >> -               pos = evlist__get_tracking_event(evlist);
> >> -               if (!evsel__is_dummy_event(pos)) {
> >> -                       /* Set up dummy event. */
> >> -                       if (evlist__add_dummy(evlist))
> >> -                               return -ENOMEM;
> >> -                       pos = evlist__last(evlist);
> >> -                       evlist__set_tracking_event(evlist, pos);
> >> -               }
> >> +               pos = evlist__findnew_tracking_event(evlist, false);
> >> +               if (!pos)
> >> +                       return -ENOMEM;
> >>
> >>                 /*
> >>                  * Enable the dummy event when the process is forked for
> >> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
> >> index 7ef43f72098e..25c3ebe2c2f5 100644
> >> --- a/tools/perf/util/evlist.c
> >> +++ b/tools/perf/util/evlist.c
> >> @@ -1694,6 +1694,24 @@ void evlist__set_tracking_event(struct evlist *evlist, struct evsel *tracking_ev
> >>         tracking_evsel->tracking = true;
> >>  }
> >>
> >> +struct evsel *evlist__findnew_tracking_event(struct evlist *evlist, bool system_wide)
> >> +{
> >> +       struct evsel *evsel;
> >> +
> >> +       evsel = evlist__get_tracking_event(evlist);
> >> +       if (!evsel__is_dummy_event(evsel)) {
> >> +               evsel = evlist__add_aux_dummy(evlist, system_wide);
> >> +               if (!evsel)
> >> +                       return NULL;
> >> +
> >> +               evlist__set_tracking_event(evlist, evsel);
> >> +       } else if (system_wide) {
> >> +               perf_evlist__go_system_wide(&evlist->core, &evsel->core);
> >> +       }
> >> +
> >> +       return evsel;
> >> +}
> >> +
> >>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str)
> >>  {
> >>         struct evsel *evsel;
> >> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
> >> index 664c6bf7b3e0..98e7ddb2bd30 100644
> >> --- a/tools/perf/util/evlist.h
> >> +++ b/tools/perf/util/evlist.h
> >> @@ -387,6 +387,7 @@ bool evlist_cpu_iterator__end(const struct evlist_cpu_iterator *evlist_cpu_itr);
> >>
> >>  struct evsel *evlist__get_tracking_event(struct evlist *evlist);
> >>  void evlist__set_tracking_event(struct evlist *evlist, struct evsel *tracking_evsel);
> >> +struct evsel *evlist__findnew_tracking_event(struct evlist *evlist, bool system_wide);
> >>
> >>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str);
> >>
> >> --
> >> 2.30.GIT
> >>
>
  

Hello,

On 2023/7/20 0:44, Ian Rogers wrote:
> On Fri, Jul 14, 2023 at 8:31 PM Yang Jihong <yangjihong1@huawei.com> wrote:
>>
>> Currently, intel-bts, intel-pt, and arm-spe may add a dummy event for
>> tracking to the evlist. We may need to search for the dummy event for
>> some settings. Therefore, add evlist__findnew_tracking_event() helper.
>>
>> evlist__findnew_tracking_event() also deal with system_wide maps if
>> system_wide is true.
> 
> I'm wondering if we can simplify the naming in the API, we have "dummy
> event" which makes sense as we literally call the event "dummy",
> "sideband" which refers to the kind of samples/events the dummy event
> will record but "tracking" I think tends to get used as a verb rather
> than a noun. So I think evlist__findnew_tracking_event should be
> evlist__findnew_dummy_event.
> 
Uh, from the discussion that followed, it seems that there is no 
consensus yet...
If there is a clear consensus on whether to use "dummy event" or 
"tracking event", I will change the name of the API.

I think sideband event is equivalent to tracking event (refer 
evsel__config(), tracking events include task, mmap, mmap2, and comm 
sideband events, which are all sideband).

tracking event are instances of dummy event. For example, we create 
another dummy event to record the text poke event of ksymbol (refer perf 
record --kcore).

An evlist contains only one tracking event, but can contain multiple 
dummy events.

Thanks,
Yang
  

On Thu, Jul 20, 2023 at 12:24 AM Yang Jihong <yangjihong1@huawei.com> wrote:
>
> Hello,
>
> On 2023/7/20 0:44, Ian Rogers wrote:
> > On Fri, Jul 14, 2023 at 8:31 PM Yang Jihong <yangjihong1@huawei.com> wrote:
> >>
> >> Currently, intel-bts, intel-pt, and arm-spe may add a dummy event for
> >> tracking to the evlist. We may need to search for the dummy event for
> >> some settings. Therefore, add evlist__findnew_tracking_event() helper.
> >>
> >> evlist__findnew_tracking_event() also deal with system_wide maps if
> >> system_wide is true.
> >
> > I'm wondering if we can simplify the naming in the API, we have "dummy
> > event" which makes sense as we literally call the event "dummy",
> > "sideband" which refers to the kind of samples/events the dummy event
> > will record but "tracking" I think tends to get used as a verb rather
> > than a noun. So I think evlist__findnew_tracking_event should be
> > evlist__findnew_dummy_event.
> >
> Uh, from the discussion that followed, it seems that there is no
> consensus yet...
> If there is a clear consensus on whether to use "dummy event" or
> "tracking event", I will change the name of the API.
>
> I think sideband event is equivalent to tracking event (refer
> evsel__config(), tracking events include task, mmap, mmap2, and comm
> sideband events, which are all sideband).
>
> tracking event are instances of dummy event. For example, we create
> another dummy event to record the text poke event of ksymbol (refer perf
> record --kcore).
>
> An evlist contains only one tracking event, but can contain multiple
> dummy events.

Thanks for the feedback. So the tracking event is by definition the
first dummy event in the evlist? What is the purpose of the other
dummy events in this case? Perhaps we can get to an intention
revealing implementation something like:

/** The "tracking event" gathering sideband data is the first dummy
event in the list. */
struct evsel *evlist__findnew_tracking_event(struct evlist *evlist)
{
   struct evsel *dummy = evlist__find_first_dummy_event(evlist);

   if (!dummy) {
      dummy = evlist__add_dummy(evlist);
   }
   return dummy;
}

But I think the key thing for me is I'm still not sure what is going
on when there are multiple dummy events for you, what are the other
dummy events for other than tracking sideband data?

Thanks,
Ian

>
> Thanks,
> Yang
  

Hello,

On 2023/7/29 0:40, Ian Rogers wrote:
> On Thu, Jul 20, 2023 at 12:24 AM Yang Jihong <yangjihong1@huawei.com> wrote:
>>
>> Hello,
>>
>> On 2023/7/20 0:44, Ian Rogers wrote:
>>> On Fri, Jul 14, 2023 at 8:31 PM Yang Jihong <yangjihong1@huawei.com> wrote:
>>>>
>>>> Currently, intel-bts, intel-pt, and arm-spe may add a dummy event for
>>>> tracking to the evlist. We may need to search for the dummy event for
>>>> some settings. Therefore, add evlist__findnew_tracking_event() helper.
>>>>
>>>> evlist__findnew_tracking_event() also deal with system_wide maps if
>>>> system_wide is true.
>>>
>>> I'm wondering if we can simplify the naming in the API, we have "dummy
>>> event" which makes sense as we literally call the event "dummy",
>>> "sideband" which refers to the kind of samples/events the dummy event
>>> will record but "tracking" I think tends to get used as a verb rather
>>> than a noun. So I think evlist__findnew_tracking_event should be
>>> evlist__findnew_dummy_event.
>>>
>> Uh, from the discussion that followed, it seems that there is no
>> consensus yet...
>> If there is a clear consensus on whether to use "dummy event" or
>> "tracking event", I will change the name of the API.
>>
>> I think sideband event is equivalent to tracking event (refer
>> evsel__config(), tracking events include task, mmap, mmap2, and comm
>> sideband events, which are all sideband).
>>
>> tracking event are instances of dummy event. For example, we create
>> another dummy event to record the text poke event of ksymbol (refer perf
>> record --kcore).
>>
>> An evlist contains only one tracking event, but can contain multiple
>> dummy events.
> 
> Thanks for the feedback. So the tracking event is by definition the
> first dummy event in the evlist? What is the purpose of the other
Uh... It may not be the first dummy event, but evsel->track must be 
true. Only one evsel in an evlist meets this condition.

> dummy events in this case? Perhaps we can get to an intention
> revealing implementation something like:
> 
> /** The "tracking event" gathering sideband data is the first dummy
> event in the list. */
> struct evsel *evlist__findnew_tracking_event(struct evlist *evlist)
> {
>     struct evsel *dummy = evlist__find_first_dummy_event(evlist);
> 
>     if (!dummy) {
>        dummy = evlist__add_dummy(evlist);
>     }
>     return dummy;
> }
> 
> But I think the key thing for me is I'm still not sure what is going
> on when there are multiple dummy events for you, what are the other
> dummy events for other than tracking sideband data?
> 
For other dummy events, perf record will open a dummy event to track 
ksymbol text_poke when "--kcore" option is used.
I thinks tracking ksymbol text_poke separately it needs to be processed 
independently, go system_wide and enable immediately.

All of the above is my understanding, may need Adrian to confirm whether 
it is accurate.

Thanks,
Yang
  

On 19/07/23 20:12, Ian Rogers wrote:
> On Wed, Jul 19, 2023 at 9:59 AM Adrian Hunter <adrian.hunter@intel.com> wrote:
>>
>> On 19/07/23 19:44, Ian Rogers wrote:
>>> On Fri, Jul 14, 2023 at 8:31 PM Yang Jihong <yangjihong1@huawei.com> wrote:
>>>>
>>>> Currently, intel-bts, intel-pt, and arm-spe may add a dummy event for
>>>> tracking to the evlist. We may need to search for the dummy event for
>>>> some settings. Therefore, add evlist__findnew_tracking_event() helper.
>>>>
>>>> evlist__findnew_tracking_event() also deal with system_wide maps if
>>>> system_wide is true.
>>>
>>> I'm wondering if we can simplify the naming in the API, we have "dummy
>>> event" which makes sense as we literally call the event "dummy",
>>> "sideband" which refers to the kind of samples/events the dummy event
>>> will record but "tracking" I think tends to get used as a verb rather
>>> than a noun. So I think evlist__findnew_tracking_event should be
>>> evlist__findnew_dummy_event.
>>
>> Except the tracking event has "tracking" set but there can be other dummy
>> events that do not.
> 
> Thanks! I'm wondering what a dummy event without tracking would be
> used for - do you have a reference?

For example, text_poke events need to be recorded on all CPUs
because changes to the kernel affect every CPU.  Another example.
it can be interesting to capture switch events CPU-wide even if
only some processes are being traced.

>                                     I don't see anything in
> perf_event.h calling things like mmap2/comm in perf_event_attr
> tracking. I'm not a fan of dummy due to it not being intention
> revealing. Perhaps if we could go back in time  we could call the
> event "sideband",

Auxiliary events are inband with respect to the perf buffer.  Only
when the "main" tracing could be considered to be the AUX area
buffer, can the events in the perf buffer be considered sideband.

>                   maybe we should migrate to this. We have other
> non-obvious uses of the term dummy like in cpumap:
> https://git.kernel.org/pub/scm/linux/kernel/git/perf/perf-tools-next.git/tree/tools/lib/perf/include/perf/cpumap.h?h=perf-tools-next#n24
> If tracking can be on any event then does that make the functions
> behavior more ambiguous if it means dummy+tracking not <any
> event>+tracking?
> 
> Thanks,
> Ian
> 
>>>
>>> Thanks,
>>> Ian
>>>
>>>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
>>>> ---
>>>>  tools/perf/builtin-record.c | 11 +++--------
>>>>  tools/perf/util/evlist.c    | 18 ++++++++++++++++++
>>>>  tools/perf/util/evlist.h    |  1 +
>>>>  3 files changed, 22 insertions(+), 8 deletions(-)
>>>>
>>>> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
>>>> index aec18db7ff23..ca83599cc50c 100644
>>>> --- a/tools/perf/builtin-record.c
>>>> +++ b/tools/perf/builtin-record.c
>>>> @@ -1295,14 +1295,9 @@ static int record__open(struct record *rec)
>>>>          */
>>>>         if (opts->target.initial_delay || target__has_cpu(&opts->target) ||
>>>>             perf_pmus__num_core_pmus() > 1) {
>>>> -               pos = evlist__get_tracking_event(evlist);
>>>> -               if (!evsel__is_dummy_event(pos)) {
>>>> -                       /* Set up dummy event. */
>>>> -                       if (evlist__add_dummy(evlist))
>>>> -                               return -ENOMEM;
>>>> -                       pos = evlist__last(evlist);
>>>> -                       evlist__set_tracking_event(evlist, pos);
>>>> -               }
>>>> +               pos = evlist__findnew_tracking_event(evlist, false);
>>>> +               if (!pos)
>>>> +                       return -ENOMEM;
>>>>
>>>>                 /*
>>>>                  * Enable the dummy event when the process is forked for
>>>> diff --git a/tools/perf/util/evlist.c b/tools/perf/util/evlist.c
>>>> index 7ef43f72098e..25c3ebe2c2f5 100644
>>>> --- a/tools/perf/util/evlist.c
>>>> +++ b/tools/perf/util/evlist.c
>>>> @@ -1694,6 +1694,24 @@ void evlist__set_tracking_event(struct evlist *evlist, struct evsel *tracking_ev
>>>>         tracking_evsel->tracking = true;
>>>>  }
>>>>
>>>> +struct evsel *evlist__findnew_tracking_event(struct evlist *evlist, bool system_wide)
>>>> +{
>>>> +       struct evsel *evsel;
>>>> +
>>>> +       evsel = evlist__get_tracking_event(evlist);
>>>> +       if (!evsel__is_dummy_event(evsel)) {
>>>> +               evsel = evlist__add_aux_dummy(evlist, system_wide);
>>>> +               if (!evsel)
>>>> +                       return NULL;
>>>> +
>>>> +               evlist__set_tracking_event(evlist, evsel);
>>>> +       } else if (system_wide) {
>>>> +               perf_evlist__go_system_wide(&evlist->core, &evsel->core);
>>>> +       }
>>>> +
>>>> +       return evsel;
>>>> +}
>>>> +
>>>>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str)
>>>>  {
>>>>         struct evsel *evsel;
>>>> diff --git a/tools/perf/util/evlist.h b/tools/perf/util/evlist.h
>>>> index 664c6bf7b3e0..98e7ddb2bd30 100644
>>>> --- a/tools/perf/util/evlist.h
>>>> +++ b/tools/perf/util/evlist.h
>>>> @@ -387,6 +387,7 @@ bool evlist_cpu_iterator__end(const struct evlist_cpu_iterator *evlist_cpu_itr);
>>>>
>>>>  struct evsel *evlist__get_tracking_event(struct evlist *evlist);
>>>>  void evlist__set_tracking_event(struct evlist *evlist, struct evsel *tracking_evsel);
>>>> +struct evsel *evlist__findnew_tracking_event(struct evlist *evlist, bool system_wide);
>>>>
>>>>  struct evsel *evlist__find_evsel_by_str(struct evlist *evlist, const char *str);
>>>>
>>>> --
>>>> 2.30.GIT
>>>>
>>