[RFC PATCH v3] perf cs-etm: Split Coresight decode by aux records

[Mathieu Poirier]

On Thu, 27 May 2021 at 07:46, James Clark <james.clark at arm.com> wrote:
>
>
>
> On 27/05/2021 13:42, James Clark wrote:
> > Populate the auxtrace queues using AUX records rather than whole
> > auxtrace buffers.
> >
> ...
> > Snapshot mode still needs to be tested.
> >
>
> Snapshot mode is also working, but needs the following patch applied to reverse aux_offset
> from the end of the buffer to the beginning:

It might be better to send another revision with this patch included
in to make sure everyone is looking at (and testing) the same thing.

>
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 5d6c03488187..9db556e14dfa 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -2700,6 +2700,7 @@ static int cs_etm__queue_aux_fragment(struct perf_session *session,
>         struct perf_record_auxtrace *auxtrace_event;
>         union perf_event auxtrace_fragment;
>         bool matchesCpuPid;
> +       __u64 aux_offset;
>         struct cs_etm_auxtrace *etm = container_of(session->auxtrace,
>                                                    struct cs_etm_auxtrace,
>                                                    auxtrace);
> @@ -2730,19 +2731,26 @@ static int cs_etm__queue_aux_fragment(struct perf_session *session,
>         else
>                 matchesCpuPid = auxtrace_event->cpu == sample->cpu;
>
> +       /*
> +        * In snapshot/overwrite mode, the head points to the end of the buffer so aux_offset needs
> +        * to have the size subtracted so it points to the beginning as in normal mode.
> +        */
> +       if (aux_event->flags && PERF_AUX_FLAG_OVERWRITE)
> +               aux_offset = aux_event->aux_offset - aux_event->aux_size;
> +       else
> +               aux_offset = aux_event->aux_offset;
> +
>         if (matchesCpuPid &&
> -           aux_event->aux_offset >= auxtrace_event->offset &&
> -           aux_event->aux_offset + aux_event->aux_size <=
> -                       auxtrace_event->offset + auxtrace_event->size) {
> +           aux_offset >= auxtrace_event->offset &&
> +           aux_offset + aux_event->aux_size <= auxtrace_event->offset + auxtrace_event->size) {
>                 /*
>                  * If this AUX event was inside this buffer somewhere, create a new auxtrace event
>                  * based on the sizes of the aux event, and queue that fragment.
>                  */
>                 auxtrace_fragment.auxtrace = *auxtrace_event;
>                 auxtrace_fragment.auxtrace.size = aux_event->aux_size;
> -               auxtrace_fragment.auxtrace.offset = aux_event->aux_offset;
> -               file_offset += aux_event->aux_offset - auxtrace_event->offset +
> -                               auxtrace_event->header.size;
> +               auxtrace_fragment.auxtrace.offset = aux_offset;
> +               file_offset += aux_offset - auxtrace_event->offset + auxtrace_event->header.size;
>                 return auxtrace_queues__add_event(&etm->queues,
>                                                session,
>                                                &auxtrace_fragment,
>
>