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SubjectRe: [RFT v2 1/4] perf cs-etm: Generate sample for missed packets
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Hi Leo,

On 21/05/18 09:52, Leo Yan wrote:
> Commit e573e978fb12 ("perf cs-etm: Inject capabilitity for CoreSight
> traces") reworks the samples generation flow from CoreSight trace to
> match the correct format so Perf report tool can display the samples
> properly. But the change has side effect for packet handling, it only
> generate samples when 'prev_packet->last_instr_taken_branch' is true,
> this results in the start tracing packet and exception packets are
> dropped.
>
> This patch checks extra two conditions for complete samples:
>
> - If 'prev_packet->sample_type' is zero we can use this condition to
> get to know this is the start tracing packet; for this case, the start
> packet's end_addr is zero as well so we need to handle it in the
> function cs_etm__last_executed_instr();
>

I think you also need to add something in to handle discontinuities in
trace - for example it is possible to configure the ETM to only trace
execution in specific code regions or to trace a few cycles every so
often. In these cases, prev_packet->sample_type will not be zero, but
whatever the previous packet was. You will get a CS_ETM_TRACE_ON packet
in such cases, generated by an I_TRACE_ON element in the trace stream.
You also get this on exception return.

However, you should also keep the test for prev_packet->sample_type == 0
as you may not see a CS_ETM_TRACE_ON when decoding a buffer that has
wrapped.

Regards

Rob

> - If 'prev_packet->exc' is true, we can know the previous packet is
> exception handling packet so need to generate sample for exception
> flow.
>
> Fixes: e573e978fb12 ("perf cs-etm: Inject capabilitity for CoreSight traces")
> Cc: Mike Leach <mike.leach@arm.com>
> Cc: Robert Walker <robert.walker@arm.com>
> Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>
> ---
> tools/perf/util/cs-etm.c | 35 ++++++++++++++++++++++++++++-------
> 1 file changed, 28 insertions(+), 7 deletions(-)
>
> diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c
> index 822ba91..378953b 100644
> --- a/tools/perf/util/cs-etm.c
> +++ b/tools/perf/util/cs-etm.c
> @@ -495,6 +495,13 @@ static inline void cs_etm__reset_last_branch_rb(struct cs_etm_queue *etmq)
> static inline u64 cs_etm__last_executed_instr(struct cs_etm_packet *packet)
> {
> /*
> + * The packet is the start tracing packet if the end_addr is zero,
> + * returns 0 for this case.
> + */
> + if (!packet->end_addr)
> + return 0;
> +
> + /*
> * The packet records the execution range with an exclusive end address
> *
> * A64 instructions are constant size, so the last executed
> @@ -897,13 +904,27 @@ static int cs_etm__sample(struct cs_etm_queue *etmq)
> etmq->period_instructions = instrs_over;
> }
>
> - if (etm->sample_branches &&
> - etmq->prev_packet &&
> - etmq->prev_packet->sample_type == CS_ETM_RANGE &&
> - etmq->prev_packet->last_instr_taken_branch) {
> - ret = cs_etm__synth_branch_sample(etmq);
> - if (ret)
> - return ret;
> + if (etm->sample_branches && etmq->prev_packet) {
> + bool generate_sample = false;
> +
> + /* Generate sample for start tracing packet */
> + if (etmq->prev_packet->sample_type == 0)
> + generate_sample = true;
> +
> + /* Generate sample for exception packet */
> + if (etmq->prev_packet->exc == true)
> + generate_sample = true;
> +
> + /* Generate sample for normal branch packet */
> + if (etmq->prev_packet->sample_type == CS_ETM_RANGE &&
> + etmq->prev_packet->last_instr_taken_branch)
> + generate_sample = true;
> +
> + if (generate_sample) {
> + ret = cs_etm__synth_branch_sample(etmq);
> + if (ret)
> + return ret;
> + }
> }
>
> if (etm->sample_branches || etm->synth_opts.last_branch) {
>

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