linux-kernel - Re: [PATCH v1 4/6] perf auxtrace: Iterate all AUX events when finish reading

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Message-ID: <951fc660-58a2-4b8a-a763-5a1e4d807c75@arm.com>
Date: Mon, 22 Jul 2024 21:52:34 +0100
From: Leo Yan <leo.yan@....com>
To: Adrian Hunter <adrian.hunter@...el.com>,
 Arnaldo Carvalho de Melo <acme@...nel.org>,
 Namhyung Kim <namhyung@...nel.org>, Ian Rogers <irogers@...gle.com>,
 James Clark <james.clark@...aro.org>,
 Suzuki K Poulose <suzuki.poulose@....com>, Mike Leach
 <mike.leach@...aro.org>, John Garry <john.g.garry@...cle.com>,
 Will Deacon <will@...nel.org>, Jiri Olsa <jolsa@...nel.org>,
 Mark Rutland <mark.rutland@....com>, coresight@...ts.linaro.org,
 linux-arm-kernel@...ts.infradead.org, linux-perf-users@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 4/6] perf auxtrace: Iterate all AUX events when finish
 reading

On 7/22/2024 4:59 PM, Adrian Hunter wrote:

[...]

>>>> @@ -670,18 +670,25 @@ static int evlist__enable_event_idx(struct evlist *evlist, struct evsel *evsel,
>>>>   int auxtrace_record__read_finish(struct auxtrace_record *itr, int idx)
>>>>   {
>>>>        struct evsel *evsel;
>>>> +     int ret = -EINVAL;
>>>>
>>>>        if (!itr->evlist || !itr->pmu)
>>>>                return -EINVAL;
>>>>
>>>>        evlist__for_each_entry(itr->evlist, evsel) {
>>>> -             if (evsel->core.attr.type == itr->pmu->type) {
>>>> +             if (evsel__is_aux_event(evsel)) {
>>>
>>> If the type is the same, then there is no need to
>>> change the logic here?
>>
>> No, the type is not same for AUX events. Every event has its own type
>> value, this is likely related to recent refactoring.
>>
>> As a result, 'itr->pmu' only maintains the first registered AUX event,
>> comparing to it the tool will find _only_ one AUX event. This is why here
>> changes to use the evsel__is_aux_event() to detect AUX event.
>>
>>> Otherwise, maybe that should be a separate patch
>>
>> Could you explain what is a separate patch for?
> 
> No need.
> 
>>
>> After this change, the field 'itr->pmu' will be redundant (at least this
>> is the case for Arm SPE). I am preparing a refactoring patches for cleaning up
>> and see if can totally remove the field 'itr->pmu' (if all AUX events
>> have no issue.
> 
> For this function, 'itr->pmu' could be removed in this patch
> since it is not used anymore.

Thanks for confirmation. I will use a separate patch for removing 'itr-pmu'
after it is not used anymore.

>>>>                        if (evsel->disabled)
>>>> -                             return 0;
>>>> -                     return evlist__enable_event_idx(itr->evlist, evsel, idx);
>>>> +                             continue;
>>>> +                     ret = evlist__enable_event_idx(itr->evlist, evsel, idx);
>>>> +                     if (ret >= 0)
>>>
>>> Should this be:
>>>
>>>                          if (ret < 0)
>>
>> Here the logic is to iterate all AUX events, even if an AUX event fails to
>> find the buffer index, it will continue to next AUX event.
>>
>> So it directly bails out for success (as we have found the matched AUX
>> event and enabled it). For the failure cause, it will continue for checking
>> next event - until all events have been checked and no event is matched
>> for buffer index, the failure will be handled at the end of the function.
> 
> Thanks for the explanation. Could probably use a small comment.

Will do.

Thanks,
Leo