Re: [RFT v2 1/4] perf cs-etm: Generate sample for missed packets

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) {