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

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Message-ID: <1cb6fdfc-0405-4bfb-acd4-ed3b24744c8b@intel.com>
Date: Mon, 22 Jul 2024 18:59:42 +0300
From: Adrian Hunter <adrian.hunter@...el.com>
To: Leo Yan <leo.yan@....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 22/07/24 18:09, Leo Yan wrote:
> On 7/22/24 12:13, Adrian Hunter wrote:
> 
> [...]
> 
>> On 21/07/24 23:21, Leo Yan wrote:
>>> When finished to read AUX trace data from mmaped buffer, based on the
>>> AUX buffer index the core layer needs to search the corresponding PMU
>>> event and re-enable it to continue tracing.
>>>
>>> However, current code only searches the first AUX event. It misses to
>>> search other enabled AUX events, thus, it returns failure if the buffer
>>> index does not belong to the first AUX event.
>>>
>>> This patch extends the auxtrace_record__read_finish() function to
>>> search for every enabled AUX events, so all the mmaped buffer indexes
>>> can be covered.
>>>
>>> Signed-off-by: Leo Yan <leo.yan@....com>
>>> ---
>>>   tools/perf/util/auxtrace.c | 15 +++++++++++----
>>>   1 file changed, 11 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
>>> index e2f317063eec..95be330d7e10 100644
>>> --- a/tools/perf/util/auxtrace.c
>>> +++ b/tools/perf/util/auxtrace.c
>>> @@ -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.

> 
>>
>>>                        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.

> 
> Thanks,
> Leo
> 
>>
>>> +                             return ret;
>>
>> And will need a common error path for the pr_err() below.
>>
>>>                }
>>>        }
>>> -     return -EINVAL;
>>> +
>>> +     if (ret < 0)
>>> +             pr_err("Failed to event enable event (idx=%d): %d\n", idx, ret);
>>> +
>>> +     return ret;
>>>   }
>>>
>>>   /*
>>