Messages in this thread | | | Subject | Re: [PATCH v2 2/7] perf evlist: Add evlist__findnew_tracking_event() helper | From | Yang Jihong <> | Date | Sat, 29 Jul 2023 10:10:59 +0800 |
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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
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