Messages in this thread | | | Subject | Re: [RFT v2 1/4] perf cs-etm: Generate sample for missed packets | From | Robert Walker <> | Date | Mon, 21 May 2018 12:27:42 +0100 |
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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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