Re: [PATCH 1/3] perf arm-spe: Track task context switch for cpu-mode events

[Leo Yan <leo.yan@linaro.org>]

Hi German,

On Tue, Nov 02, 2021 at 06:07:37PM +0000, German Gomez wrote:
> When perf report synthesize events from ARM SPE data, it refers to
> current cpu, pid and tid in the machine.  But there's no place to set
> them in the ARM SPE decoder.  I'm seeing all pid/tid is set to -1 and
> user symbols are not resolved in the output.
> 
>   # perf record -a -e arm_spe_0/ts_enable=1/ sleep 1
> 
>   # perf report -q | head
>      8.77%     8.77%  :-1      [kernel.kallsyms]  [k] format_decode
>      7.02%     7.02%  :-1      [kernel.kallsyms]  [k] seq_printf
>      7.02%     7.02%  :-1      [unknown]          [.] 0x0000ffff9f687c34
>      5.26%     5.26%  :-1      [kernel.kallsyms]  [k] vsnprintf
>      3.51%     3.51%  :-1      [kernel.kallsyms]  [k] string
>      3.51%     3.51%  :-1      [unknown]          [.] 0x0000ffff9f66ae20
>      3.51%     3.51%  :-1      [unknown]          [.] 0x0000ffff9f670b3c
>      3.51%     3.51%  :-1      [unknown]          [.] 0x0000ffff9f67c040
>      1.75%     1.75%  :-1      [kernel.kallsyms]  [k] ___cache_free
>      1.75%     1.75%  :-1      [kernel.kallsyms]  [k]
> __count_memcg_events
> 
> Like Intel PT, add context switch records to track task info.  As ARM
> SPE support was added later than PERF_RECORD_SWITCH_CPU_WIDE, I think
> we can safely set the attr.context_switch bit and use it.
> 
> Signed-off-by: Namhyung Kim <namhyung@kernel.org>
> Signed-off-by: German Gomez <german.gomez@arm.com>

Reviewed-by: Leo Yan <leo.yan@linaro.org>

Note for one thing, please keep "Namhyung Kim" as the author for this
patch, thanks.

Leo

> ---
>  tools/perf/arch/arm64/util/arm-spe.c |  6 +++++-
>  tools/perf/util/arm-spe.c            | 25 +++++++++++++++++++++++++
>  2 files changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/perf/arch/arm64/util/arm-spe.c b/tools/perf/arch/arm64/util/arm-spe.c
> index a4420d4df..58ba8d15c 100644
> --- a/tools/perf/arch/arm64/util/arm-spe.c
> +++ b/tools/perf/arch/arm64/util/arm-spe.c
> @@ -166,8 +166,12 @@ static int arm_spe_recording_options(struct auxtrace_record *itr,
>  	tracking_evsel->core.attr.sample_period = 1;
>  
>  	/* In per-cpu case, always need the time of mmap events etc */
> -	if (!perf_cpu_map__empty(cpus))
> +	if (!perf_cpu_map__empty(cpus)) {
>  		evsel__set_sample_bit(tracking_evsel, TIME);
> +		evsel__set_sample_bit(tracking_evsel, CPU);
> +		/* also track task context switch */
> +		tracking_evsel->core.attr.context_switch = 1;
> +	}
>  
>  	return 0;
>  }
> diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
> index 58b7069c5..230bc7ab2 100644
> --- a/tools/perf/util/arm-spe.c
> +++ b/tools/perf/util/arm-spe.c
> @@ -681,6 +681,25 @@ static int arm_spe_process_timeless_queues(struct arm_spe *spe, pid_t tid,
>  	return 0;
>  }
>  
> +static int arm_spe_context_switch(struct arm_spe *spe, union perf_event *event,
> +				  struct perf_sample *sample)
> +{
> +	pid_t pid, tid;
> +	int cpu;
> +
> +	if (!(event->header.misc & PERF_RECORD_MISC_SWITCH_OUT))
> +		return 0;
> +
> +	pid = event->context_switch.next_prev_pid;
> +	tid = event->context_switch.next_prev_tid;
> +	cpu = sample->cpu;
> +
> +	if (tid == -1)
> +		pr_warning("context_switch event has no tid\n");
> +
> +	return machine__set_current_tid(spe->machine, cpu, pid, tid);
> +}
> +
>  static int arm_spe_process_event(struct perf_session *session,
>  				 union perf_event *event,
>  				 struct perf_sample *sample,
> @@ -718,6 +737,12 @@ static int arm_spe_process_event(struct perf_session *session,
>  		}
>  	} else if (timestamp) {
>  		err = arm_spe_process_queues(spe, timestamp);
> +		if (err)
> +			return err;
> +
> +		if (event->header.type == PERF_RECORD_SWITCH_CPU_WIDE ||
> +		    event->header.type == PERF_RECORD_SWITCH)
> +			err = arm_spe_context_switch(spe, event, sample);
>  	}
>  
>  	return err;
> -- 
> 2.25.1
>