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SubjectRe: [PATCH 3/7] perf cs-etm: Save aux records in each etm queue
On Fri, Feb 12, 2021 at 04:45:09PM +0200, James Clark wrote:
> The aux records will be used set the bounds of decoding in a
> later commit. In the future we may also want to use the flags
> of each record to control decoding.
>
> Do these need to be saved in their entirety, or can pointers
> to each record safely be saved instead for later access?

Rather than introudcing the perf record list, I just wander if we can
use easier method to fix this problem. So below is the rough idea
(though I don't really verify it):

The essential information we need is what's the valid buffer length can
be used for decoding. Though cs_etm_queue::buf_len tracks the buffer
length, but it's the buffer length is for the whole AUX buffer, and
which belongs to multiple "PERF_RECORD_AUX" events. So we cannot decode
at once for the whole trace data in the AUX trace buffer, on the other
hand, the incoming "PERF_RECORD_AUX" event can guide the CoreSight
decoder it should decode how much buffer size. At the end, the trace
data can be decoded step by step based on the incoming "PERF_RECORD_AUX"
events.

I'd like to propose to add a new field "cs_etm_queue::buf_rec_len", it
stands for the record length based on the RECORD_AUX event. In
theory, this value should be always less than "cs_etm_queue::buf_len".

When every time the "PERF_RECORD_AUX" event is coming, we find out the
corresponding queue (so this can be applied for "1:1" or "N:1" models
for source and sink), and accumulate "perf_record_aux::aux_size" into
"cs_etm_queue::buf_rec_len".

At the decoder side, it decreases "etmq->buf_rec_len" until to zero for
the current round of decoding (see cs_etm__decode_data_block()). Since
all the "PERF_RECORD_AUX" event will be processed before
"PERF_RECORD_EXIT" event, so we don't worry the tail trace data will be
ignored.

The main reason for this suggestion is it don't need to change the
significant logic in current code. I will try to do experiment for this
idea and share back.

James, if you think I miss anything, please correct me as needed.
Thanks!

Leo

> Signed-off-by: James Clark <james.clark@arm.com>
> ---
> tools/perf/util/cs-etm.c | 32 +++++++++++++++++++++++++++++---
> 1 file changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 8f8b448632fb..88b541b2a804 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -92,12 +92,16 @@ struct cs_etm_queue {
> /* Conversion between traceID and index in traceid_queues array */
> struct intlist *traceid_queues_list;
> struct cs_etm_traceid_queue **traceid_queues;
> + int aux_record_list_len;
> + int aux_record_list_idx;
> + struct perf_record_aux *aux_record_list;
> };
>
> /* RB tree for quick conversion between traceID and metadata pointers */
> static struct intlist *traceid_list;
>
> -static int cs_etm__update_queues(struct cs_etm_auxtrace *etm, int cpu);
> +static int cs_etm__update_queues(struct cs_etm_auxtrace *etm, int cpu,
> + struct perf_record_aux *aux_record);
> static int cs_etm__process_queues(struct cs_etm_auxtrace *etm);
> static int cs_etm__process_timeless_queues(struct cs_etm_auxtrace *etm,
> pid_t tid);
> @@ -585,6 +589,7 @@ static void cs_etm__free_queue(void *priv)
>
> cs_etm_decoder__free(etmq->decoder);
> cs_etm__free_traceid_queues(etmq);
> + free(etmq->aux_record_list);
> free(etmq);
> }
>
> @@ -759,6 +764,19 @@ static struct cs_etm_queue *cs_etm__alloc_queue(struct cs_etm_auxtrace *etm)
> return NULL;
> }
>
> +static int cs_etm__save_aux_record(struct cs_etm_queue *etmq,
> + struct perf_record_aux *aux_record)
> +{
> + etmq->aux_record_list = reallocarray(etmq->aux_record_list,
> + etmq->aux_record_list_len+1,
> + sizeof(*etmq->aux_record_list));
> + if (!etmq->aux_record_list)
> + return -ENOMEM;
> +
> + etmq->aux_record_list[etmq->aux_record_list_len++] = *aux_record;
> + return 0;
> +}
> +
> static int cs_etm__search_first_timestamp(struct cs_etm_queue *etmq)
> {
> int ret = 0;
> @@ -865,7 +883,7 @@ static int cs_etm__setup_queues(struct cs_etm_auxtrace *etm)
> return 0;
> }
>
> -static int cs_etm__update_queues(struct cs_etm_auxtrace *etm, int cpu)
> +static int cs_etm__update_queues(struct cs_etm_auxtrace *etm, int cpu, struct perf_record_aux *aux)
> {
> int ret;
> if (etm->queues.new_data) {
> @@ -875,6 +893,14 @@ static int cs_etm__update_queues(struct cs_etm_auxtrace *etm, int cpu)
> return ret;
> }
>
> + /* In timeless mode, cpu is set to -1, and a single aux buffer is filled */
> + if (cpu < 0)
> + cpu = 0;
> +
> + ret = cs_etm__save_aux_record(etm->queues.queue_array[cpu].priv, aux);
> + if (ret)
> + return ret;
> +
> if (!etm->timeless_decoding)
> return cs_etm__search_first_timestamp(etm->queues.queue_array[cpu].priv);
> else
> @@ -2357,7 +2383,7 @@ static int cs_etm__process_event(struct perf_session *session,
>
> if ((timestamp || etm->timeless_decoding)
> && event->header.type == PERF_RECORD_AUX) {
> - err = cs_etm__update_queues(etm, sample->cpu);
> + err = cs_etm__update_queues(etm, sample->cpu, &event->aux);
> if (err)
> return err;
> }
> --
> 2.28.0
>

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