Re: [PATCH 1/7] perf: cs-etm: Fix timeless decode mode detection

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 24/04/2023 14:47, James Clark wrote:
> In this context, timeless refers to the trace data rather than the perf
> event data. But when detecting whether there are timestamps in the trace
> data or not, the presence of a timestamp flag on any perf event is used.
> 
> Since commit f42c0ce573df ("perf record: Always get text_poke events
> with --kcore option") timestamps were added to a tracking event when
> --kcore is used which breaks this detection mechanism. Fix it by
> detecting if trace timestamps exist by looking at the ETM config flags.
> This would have always been a more accurate way of doing it anyway.
> 
> This fixes the following error message when using --kcore with
> Coresight:
> 
>    $ perf record --kcore -e cs_etm// --per-thread
>    $ perf report
>    The perf.data/data data has no samples!
> 
> Fixes: f42c0ce573df ("perf record: Always get text_poke events with --kcore option")
> Reported-by: Yang Shi <shy828301@gmail.com>
> Link: https://lore.kernel.org/lkml/CAHbLzkrJQTrYBtPkf=jf3OpQ-yBcJe7XkvQstX9j2frz4WF-SQ@mail.gmail.com/
> Signed-off-by: James Clark <james.clark@arm.com>
> ---
>   tools/perf/util/cs-etm.c | 30 ++++++++++++++++++------------
>   1 file changed, 18 insertions(+), 12 deletions(-)
> 
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 8dd81ddd9e4e..50593289d53c 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -2684,26 +2684,29 @@ static int cs_etm__process_auxtrace_event(struct perf_session *session,
>   	return 0;
>   }
>   
> -static bool cs_etm__is_timeless_decoding(struct cs_etm_auxtrace *etm)
> +static int cs_etm__setup_timeless_decoding(struct cs_etm_auxtrace *etm)

minor nit: "setup" sound more like prepare to do what is required to
do a timeless decoding, while we are doing more like, check if we
have to do a timeless decoding. So may be:

cs_etm_check_timeless_decoding() ?

>   {
>   	struct evsel *evsel;
>   	struct evlist *evlist = etm->session->evlist;
> -	bool timeless_decoding = true;
>   
>   	/* Override timeless mode with user input from --itrace=Z */
> -	if (etm->synth_opts.timeless_decoding)
> -		return true;
> +	if (etm->synth_opts.timeless_decoding) {
> +		etm->timeless_decoding = true;
> +		return 0;
> +	}
>   
>   	/*
> -	 * Circle through the list of event and complain if we find one
> -	 * with the time bit set.
> +	 * Find the cs_etm evsel and look at what its timestamp setting was
>   	 */
> -	evlist__for_each_entry(evlist, evsel) {
> -		if ((evsel->core.attr.sample_type & PERF_SAMPLE_TIME))
> -			timeless_decoding = false;
> -	}
> +	evlist__for_each_entry(evlist, evsel)

minor nit: please retain the braces

> +		if (cs_etm__evsel_is_auxtrace(etm->session, evsel)) {
> +			etm->timeless_decoding =
> +				!(evsel->core.attr.config & BIT(ETM_OPT_TS));


> +			return 0;
> +		}

Otherwise, looks good to me

Suzuki