[PATCH v2 4/4] perf arm-spe: Support hardware-based PID tracing

[Namhyung Kim]

On Tue, Nov 9, 2021 at 3:50 AM German Gomez <german.gomez at arm.com> wrote:
>
> If Arm SPE traces contain CONTEXT packets with TID info, use these
> values for tracking tid of samples. Otherwise fall back to using context
> switch events and display a message warning the user of possible timing
> inaccuracies [1].
>
> [1] https://lore.kernel.org/lkml/f877cfa6-9b25-6445-3806-ca44a4042eaf@arm.com/
>
> Signed-off-by: German Gomez <german.gomez at arm.com>
> ---
>  tools/perf/util/arm-spe.c | 99 +++++++++++++++++++++++++++------------
>  1 file changed, 70 insertions(+), 29 deletions(-)
>
> diff --git a/tools/perf/util/arm-spe.c b/tools/perf/util/arm-spe.c
> index 230bc7ab2..30b8bb48a 100644
> --- a/tools/perf/util/arm-spe.c
> +++ b/tools/perf/util/arm-spe.c
> @@ -71,6 +71,7 @@ struct arm_spe {
>         u64                             kernel_start;
>
>         unsigned long                   num_events;
> +       u8                              use_ctx_pkt_for_pid;
>  };
>
>  struct arm_spe_queue {
> @@ -226,6 +227,44 @@ static inline u8 arm_spe_cpumode(struct arm_spe *spe, u64 ip)
>                 PERF_RECORD_MISC_USER;
>  }
>
> +static void arm_spe_set_pid_tid_cpu(struct arm_spe *spe,
> +                                   struct auxtrace_queue *queue)
> +{
> +       struct arm_spe_queue *speq = queue->priv;
> +       pid_t tid;
> +
> +       tid = machine__get_current_tid(spe->machine, speq->cpu);
> +       if (tid != -1) {
> +               speq->tid = tid;
> +               thread__zput(speq->thread);
> +       } else
> +               speq->tid = queue->tid;
> +
> +       if ((!speq->thread) && (speq->tid != -1)) {
> +               speq->thread = machine__find_thread(spe->machine, -1,
> +                                                   speq->tid);
> +       }
> +
> +       if (speq->thread) {
> +               speq->pid = speq->thread->pid_;
> +               if (queue->cpu == -1)
> +                       speq->cpu = speq->thread->cpu;
> +       }
> +}
> +
> +static int arm_spe_set_tid(struct arm_spe_queue *speq, pid_t tid)
> +{
> +       struct arm_spe *spe = speq->spe;
> +       int err = machine__set_current_tid(spe->machine, speq->cpu, tid, tid);

I think we should pass -1 as pid as we don't know the real pid.

Thanks,
Namhyung


> +
> +       if (err)
> +               return err;
> +
> +       arm_spe_set_pid_tid_cpu(spe, &spe->queues.queue_array[speq->queue_nr]);
> +
> +       return 0;
> +}
> +