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

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Message-ID: <2a7f6d40-6502-d389-f691-488e3d9b9005@arm.com>
Date:   Mon, 4 Sep 2023 16:25:38 +0100
From:   James Clark <james.clark@....com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.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>,
        Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.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 2/2] perf cs-etm: Respect timestamp option



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@...aro.org>

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

> ---
>  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)