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

From: Leo Yan
Date: Fri Nov 05 2021 - 23:29:25 EST


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@xxxxxxxxxx>
> Signed-off-by: German Gomez <german.gomez@xxxxxxx>

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

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
>