[PATCH 2/4] perf cs-etm: Use previous thread for branch sample source IP

[Mike Leach]

On Wed, 24 May 2023 at 14:20, James Clark <james.clark at arm.com> wrote:
>
> Branch samples currently use the IP of the previous packet as the from
> IP, and the IP of the current packet as the to IP. But it incorrectly
> uses the current thread. In some cases like a jump into a different
> exception level this will attribute to the incorrect process.
>
> Fix it by tracking the previous thread in the same way the previous
> packet is tracked.
>
> Signed-off-by: James Clark <james.clark at arm.com>
> ---
>  tools/perf/util/cs-etm.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index ebffc9052561..a997fe79d458 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -86,6 +86,7 @@ struct cs_etm_traceid_queue {
>         size_t last_branch_pos;
>         union perf_event *event_buf;
>         struct thread *thread;
> +       struct thread *prev_thread;
>         struct branch_stack *last_branch;
>         struct branch_stack *last_branch_rb;
>         struct cs_etm_packet *prev_packet;
> @@ -480,6 +481,7 @@ static int cs_etm__init_traceid_queue(struct cs_etm_queue *etmq,
>         tidq->trace_chan_id = trace_chan_id;
>         tidq->thread = machine__findnew_thread(&etm->session->machines.host, -1,
>                                                queue->tid);
> +       tidq->prev_thread = machine__idle_thread(&etm->session->machines.host);
>
>         tidq->packet = zalloc(sizeof(struct cs_etm_packet));
>         if (!tidq->packet)
> @@ -616,6 +618,8 @@ static void cs_etm__packet_swap(struct cs_etm_auxtrace *etm,
>                 tmp = tidq->packet;
>                 tidq->packet = tidq->prev_packet;
>                 tidq->prev_packet = tmp;
> +               thread__put(tidq->prev_thread);
> +               tidq->prev_thread = thread__get(tidq->thread);
>         }
>  }
>
> @@ -791,6 +795,7 @@ static void cs_etm__free_traceid_queues(struct cs_etm_queue *etmq)
>                 /* Free this traceid_queue from the array */
>                 tidq = etmq->traceid_queues[idx];
>                 thread__zput(tidq->thread);
> +               thread__zput(tidq->prev_thread);
>                 zfree(&tidq->event_buf);
>                 zfree(&tidq->last_branch);
>                 zfree(&tidq->last_branch_rb);
> @@ -1450,8 +1455,8 @@ static int cs_etm__synth_branch_sample(struct cs_etm_queue *etmq,
>         sample.time = cs_etm__resolve_sample_time(etmq, tidq);
>
>         sample.ip = ip;
> -       sample.pid = tidq->thread->pid_;
> -       sample.tid = tidq->thread->tid;
> +       sample.pid = tidq->prev_thread->pid_;
> +       sample.tid = tidq->prev_thread->tid;
>         sample.addr = cs_etm__first_executed_instr(tidq->packet);
>         sample.id = etmq->etm->branches_id;
>         sample.stream_id = etmq->etm->branches_id;
> --
> 2.34.1
>

Reviewed-by: Mike Leach <mike.leach at linaro.org>

-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK