Re: [PATCH v1 2/2] perf cs-etm: Respect timestamp option

[James Clark]

On 27/08/2023 14:35, Leo Yan wrote:
> When users pass the option '--timestamp' or '-T' in the record command,
> all events will set the PERF_SAMPLE_TIME bit in the attribution.  In
> this case, the AUX event will record the kernel timestamp, but it
> doesn't mean Arm CoreSight enables timestamp packets in its hardware
> tracing.
> 
> If the option '--timestamp' or '-T' is set, this patch always enables
> Arm CoreSight timestamp, as a result, the bit 28 in event's config is to
> be set.
> 
> Before:
> 
>   # perf record -e cs_etm// --per-thread --timestamp -- ls
>   # perf script --header-only
>   ...
>   # event : name = cs_etm//, , id = { 69 }, type = 12, size = 136,
>   config = 0, { sample_period, sample_freq } = 1,
>   sample_type = IP|TID|TIME|CPU|IDENTIFIER, read_format = ID|LOST,
>   disabled = 1, enable_on_exec = 1, sample_id_all = 1, exclude_guest = 1
>   ...
> 
> After:
> 
>   # perf record -e cs_etm// --per-thread --timestamp -- ls
>   # perf script --header-only
>   ...
>   # event : name = cs_etm//, , id = { 49 }, type = 12, size = 136,
>   config = 0x10000000, { sample_period, sample_freq } = 1,
>   sample_type = IP|TID|TIME|CPU|IDENTIFIER, read_format = ID|LOST,
>   disabled = 1, enable_on_exec = 1, sample_id_all = 1, exclude_guest = 1
>   ...
> 
> Signed-off-by: Leo Yan <leo.yan@xxxxxxxxxx>

Reviewed-by: James Clark <james.clark@xxxxxxx>

> ---
>  tools/perf/arch/arm/util/cs-etm.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/tools/perf/arch/arm/util/cs-etm.c b/tools/perf/arch/arm/util/cs-etm.c
> index cf9ef9ba800b..58c506e9788d 100644
> --- a/tools/perf/arch/arm/util/cs-etm.c
> +++ b/tools/perf/arch/arm/util/cs-etm.c
> @@ -442,6 +442,15 @@ static int cs_etm_recording_options(struct auxtrace_record *itr,
>  					   "contextid", 1);
>  	}
>  
> +	/*
> +	 * When the option '--timestamp' or '-T' is enabled, the PERF_SAMPLE_TIME
> +	 * bit is set for all events.  In this case, always enable Arm CoreSight
> +	 * timestamp tracing.
> +	 */
> +	if (opts->sample_time_set)
> +		evsel__set_config_if_unset(cs_etm_pmu, cs_etm_evsel,
> +					   "timestamp", 1);
> +
>  	/* Add dummy event to keep tracking */
>  	err = parse_event(evlist, "dummy:u");
>  	if (err)