[PATCH v1 3/5] perf cs-etm: Support for NO_SYNC packet

Mathieu Poirier
2018-11-19T18:27:59Z

On Sun, Nov 11, 2018 at 12:59:41PM +0800, Leo Yan wrote:
> As described in OpenCSD (CoreSight decoder lib), in the decoding stream
> it includes one trace element with type OCSD_GEN_TRC_ELEM_NO_SYNC; the
> element indicates 'either at start of decode, or after overflow / bad
> packet', we should take it as a signal for the tracing off and this will
> cause tracing discontinuity. From the trace dump with 'perf script',
> sometimes the element OCSD_GEN_TRC_ELEM_NO_SYNC collaborates with
> element OCSD_GEN_TRC_ELEM_TRACE_ON to show the tracing flow have been
> turned off and on, in this case the cs-etm code has handled TRACE_ON
> packet well so we observe the tracing discontinuity; but in another case
> it only inserts the element OCSD_GEN_TRC_ELEM_NO_SYNC into instructions
> packets, we miss to handle the case if has only standalone NO_SYNC
> element and users cannot receive the info for tracing discontinuity.
>
> This patch introduces new type CS_ETM_TRACE_OFF to generate packet for
> receiving element OCSD_GEN_TRC_ELEM_NO_SYNC from decoder; when generate
> sample, CS_ETM_TRACE_OFF packet has almost the same behaviour with

Here you have used the word "almost", leading me to beleive there are cases
where the handling of TRACE_ON and NO_SYNC packets differ, but the
implementation enacts the same behavior for both.

Mike or Robert, can you confirm that TRACE_ON and NO_SYNC packets should be
treated the same way?

Leo, if handling of the TRACE_ON and NO_SYNC packets is the same then we should
treat them the same way in cs_etm_decoder__gen_trace_elem_printer(), i.e simply
call cs_etm_decoder__buffer_trace_on(). That way packet handling in cs-etm.c
doesn't change. Otherwise see my comments below.

> CS_ETM_TRACE_ON packet: both of them invokes cs_etm__flush() to generate
> samples for the previous instructions packet, and in cs_etm__sample() it
> also needs to generate samples if TRACE_OFF packet is followed by one
> sequential instructions packet. This patch also converts the address to
> 0 for TRACE_OFF packet, this is same with TRACE_ON packet as well.
>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
> tools/perf/util/cs-etm-decoder/cs-etm-decoder.c | 10 ++++++++++
> tools/perf/util/cs-etm-decoder/cs-etm-decoder.h | 7 ++++---
> tools/perf/util/cs-etm.c | 15 +++++++++++----
> 3 files changed, 25 insertions(+), 7 deletions(-)
>
> diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> index 5efb616..9d52727 100644
> --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.c
> @@ -369,6 +369,14 @@ cs_etm_decoder__buffer_range(struct cs_etm_decoder *decoder,
> }
>
> static ocsd_datapath_resp_t
> +cs_etm_decoder__buffer_trace_off(struct cs_etm_decoder *decoder,
> + const uint8_t trace_chan_id)
> +{
> + return cs_etm_decoder__buffer_packet(decoder, trace_chan_id,
> + CS_ETM_TRACE_OFF);
> +}
> +
> +static ocsd_datapath_resp_t
> cs_etm_decoder__buffer_trace_on(struct cs_etm_decoder *decoder,
> const uint8_t trace_chan_id)
> {
> @@ -389,6 +397,8 @@ static ocsd_datapath_resp_t cs_etm_decoder__gen_trace_elem_printer(
> case OCSD_GEN_TRC_ELEM_UNKNOWN:
> break;
> case OCSD_GEN_TRC_ELEM_NO_SYNC:
> + resp = cs_etm_decoder__buffer_trace_off(decoder,
> + trace_chan_id);

If we want to handle NO_SYNC element types, why introduce a "trace_off"
function? Wouldn't it make more sense to call it
cs_etm_decoder__buffer_no_sync() ?

> decoder->trace_on = false;
> break;
> case OCSD_GEN_TRC_ELEM_TRACE_ON:
> diff --git a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
> index 9351bd1..a38c97c 100644
> --- a/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
> +++ b/tools/perf/util/cs-etm-decoder/cs-etm-decoder.h
> @@ -23,9 +23,10 @@ struct cs_etm_buffer {
> };
>
> enum cs_etm_sample_type {
> - CS_ETM_EMPTY = 0,
> - CS_ETM_RANGE = 1 << 0,
> - CS_ETM_TRACE_ON = 1 << 1,
> + CS_ETM_EMPTY = 0,
> + CS_ETM_RANGE = 1 << 0,
> + CS_ETM_TRACE_ON = 1 << 1,
> + CS_ETM_TRACE_OFF = 1 << 2,

CS_ETM_NO_SYNC, see above comment. And please don't use indentation.

> };
>
> enum cs_etm_isa {
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index f4fa877..2a0cef9 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -517,8 +517,9 @@ static inline int cs_etm__t32_instr_size(struct cs_etm_queue *etmq,
>
> static inline u64 cs_etm__first_executed_instr(struct cs_etm_packet *packet)
> {
> - /* Returns 0 for the CS_ETM_TRACE_ON packet */
> - if (packet->sample_type == CS_ETM_TRACE_ON)
> + /* Returns 0 for TRACE_ON and TRACE_OFF packets */
> + if (packet->sample_type == CS_ETM_TRACE_ON ||
> + packet->sample_type == CS_ETM_TRACE_OFF)
> return 0;
>
> return packet->start_addr;
> @@ -527,8 +528,9 @@ static inline u64 cs_etm__first_executed_instr(struct cs_etm_packet *packet)
> static inline
> u64 cs_etm__last_executed_instr(const struct cs_etm_packet *packet)
> {
> - /* Returns 0 for the CS_ETM_TRACE_ON packet */
> - if (packet->sample_type == CS_ETM_TRACE_ON)
> + /* Returns 0 for TRACE_ON and TRACE_OFF packets */
> + if (packet->sample_type == CS_ETM_TRACE_ON ||
> + packet->sample_type == CS_ETM_TRACE_OFF)
> return 0;
>
> return packet->end_addr - packet->last_instr_size;
> @@ -930,6 +932,10 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
> if (etmq->prev_packet->sample_type == CS_ETM_TRACE_ON)
> generate_sample = true;
>
> + /* Generate sample for tracing off packet */
> + if (etmq->prev_packet->sample_type == CS_ETM_TRACE_OFF)
> + generate_sample = true;
> +
> /* Generate sample for branch taken packet */
> if (etmq->prev_packet->sample_type == CS_ETM_RANGE &&
> etmq->prev_packet->last_instr_taken_branch)
> @@ -1085,6 +1091,7 @@ static int cs_etm__run_decoder(struct cs_etm_queue *etmq)
> cs_etm__sample(etmq);
> break;
> case CS_ETM_TRACE_ON:
> + case CS_ETM_TRACE_OFF:
> /*
> * Discontinuity in trace, flush
> * previous branch stack
> --
> 2.7.4
>