Re: [PATCH v2 1/4] perf auxtrace: Iterate all AUX events when finish reading

[Adrian Hunter <adrian.hunter@intel.com>]

On 25/07/24 09:46, Leo Yan wrote:
> When finished to read AUX trace data from mmaped buffer, based on the

Here and elsewhere 'mmapped' is more common than 'mmaped' so maybe:

	mmaped -> mmapped

> 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.

Looking at this again, a couple more things came to mind - see below.

> 
> Signed-off-by: Leo Yan <leo.yan@arm.com>
> ---
>  tools/perf/util/auxtrace.c | 25 ++++++++++++++++++++-----
>  1 file changed, 20 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
> index b99e72f7da88..61835a6a9ea3 100644
> --- a/tools/perf/util/auxtrace.c
> +++ b/tools/perf/util/auxtrace.c
> @@ -670,18 +670,33 @@ 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)
> +	if (!itr->evlist)
>  		return -EINVAL;
>  
>  	evlist__for_each_entry(itr->evlist, evsel) {
> -		if (evsel->core.attr.type == itr->pmu->type) {
> +		if (evsel__is_aux_event(evsel)) {
>  			if (evsel->disabled)
> -				return 0;
> -			return evlist__enable_event_idx(itr->evlist, evsel, idx);
> +				continue;

That will make the evsel->disabled case an error, which
might be a problem. Possibly the event can be disabled
(e.g. via control fifo) but still have data to read out.

> +			/*
> +			 * Multiple AUX events might be opened in a session.
> +			 * Bail out for success case as the AUX event has been
> +			 * found and enabled, otherwise, continue to check if
> +			 * the next AUX event can cover the mmaped buffer with
> +			 * 'idx'.
> +			 */

Thinking about this some more, raised some questions:

How do we know there is only one AUX event per mmap?  They
would have to be on different CPUs for that to be true?
And wouldn't --per-thread have all AUX events in every mmap?

> +			ret = evlist__enable_event_idx(itr->evlist, evsel, idx);
> +			if (ret >= 0)
> +				return ret;
>  		}
>  	}
> -	return -EINVAL;
> +
> +	/* Failed to find an event for the buffer 'idx' */
> +	if (ret < 0)
> +		pr_err("Failed to enable event (idx=%d): %d\n", idx, ret);
> +
> +	return ret;
>  }
>  
>  /*