Messages in this thread | | | Date | Fri, 4 Jun 2021 13:21:17 +0800 | From | Leo Yan <> | Subject | Re: [RFC PATCH v4 1/1] perf cs-etm: Split Coresight decode by aux records |
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Hi James,
On Tue, Jun 01, 2021 at 04:07:51PM +0300, James Clark wrote: > Populate the auxtrace queues using AUX records rather than whole > auxtrace buffers. > > This is similar to the auxtrace_queues__process_index() -> > auxtrace_queues__add_indexed_event() flow where > perf_session__peek_event() is used to read AUXTRACE events out of random > positions in the file based on the auxtrace index. > > Now there is a second pass using perf_session__peek_events() which loops > over all PERF_RECORD_AUX events, finds the corresponding auxtrace > buffer, and adds a fragment of that buffer to the auxtrace queues, > rather than the whole buffer. > > This is a completely new implementation compared to v1 and v2 of the > patchset where significant modifications were made to the decoding flow, > including saving all of the AUX records, and changing the point where > decoding started. These changes had effects on the outcome of decoding, > but with this implementation, the output of decoding is identical to > perf/core, except in the case where decoding failed due to the issue > that this change addresses. No changes to decoding were made, apart > from populating the auxtrace queues.
IMHO, this patch is much better than previous versions! :)
When went through the whole patch, the most code actually is general enough and can consider to place into into util/auxtrace.c. If there have any objection, we can come back to add the code for only cs-etm specific.
> Because the decoder is already reset between each auxtrace buffer, > populating the queues with fragments of whole buffers based on AUX > records has the same affect as resetting the decoder on the AUX record > bounds during decode. But this approach only requires a change to one > part of the whole flow, rather than many parts. > > There is still one TODO about how buffers are found. Currently there is > a plain loop as a search, but this could be improved with a binary > search or keeping a record of which buffers have already been added and > starting the search from the last used place. AUX records and buffers > will come in similar orders in the file so the latter would be simpler > and probably be good enough. But I'm looking for feedback about the > approach as a whole before ironing out all of the details. > > Other issues that were fixed by the previous patchsets such as fixing > the case where the first aux record comes before the first MMAP record > can now be fixed as completely independent issues. > > Testing > ======= > > Testing was done with the following script, to diff the decoding results > between the patched and un-patched versions of perf: > > #!/bin/bash > set -ex > > $1 script -i $3 $4 > split.script > $2 script -i $3 $4 > default.script > > diff split.script default.script | head -n 20 > > And it was run like this, with various itrace options depending on the > quantity of synthesised events: > > compare.sh ./perf-patched ./perf-default perf-per-cpu-2-threads.data --itrace=i100000ns > > No changes in output were observed in the following scenarios: > > * Simple per-cpu > perf record -e cs_etm/@tmc_etr0/u top > > * Per-thread, single thread > perf record -e cs_etm/@tmc_etr0/u --per-thread ./threads_C > > * Per-thread multiple threads (but only one thread collected data): > perf record -e cs_etm/@tmc_etr0/u --per-thread --pid 4596,4597 > > * Per-thread multiple threads (both threads collected data): > perf record -e cs_etm/@tmc_etr0/u --per-thread --pid 4596,4597 > > * Per-cpu explicit threads: > perf record -e cs_etm/@tmc_etr0/u --pid 853,854 > > * System-wide (per-cpu): > perf record -e cs_etm/@tmc_etr0/u -a > > * No data collected (no aux buffers) > Can happen with any command when run for a short period > > * Containing truncated records > Can happen with any command > > * Containing aux records with 0 size > Can happen with any command > > * Snapshot mode > perf record -e cs_etm/@tmc_etr0/u -a --snapshot > > Signed-off-by: James Clark <james.clark@arm.com> > --- > tools/perf/util/cs-etm.c | 159 ++++++++++++++++++++++++++++++++++++++- > 1 file changed, 156 insertions(+), 3 deletions(-) > > diff --git a/tools/perf/util/cs-etm.c b/tools/perf/util/cs-etm.c > index 64536a6ed10a..053aad4b28cf 100644 > --- a/tools/perf/util/cs-etm.c > +++ b/tools/perf/util/cs-etm.c > @@ -2679,6 +2679,161 @@ static u64 *cs_etm__create_meta_blk(u64 *buff_in, int *buff_in_offset, > return metadata; > } > > +/** > + * Puts a fragment of an auxtrace buffer into the auxtrace queues based > + * on the bounds of aux_event, if it matches with the buffer that's at > + * file_offset. > + * > + * Normally, whole auxtrace buffers would be added to the queue. But we > + * want to reset the decoder for every PERF_RECORD_AUX event, and the decoder > + * is reset across each buffer, so splitting the buffers up in advance has > + * the same effect. > + */ > +static int cs_etm__queue_aux_fragment(struct perf_session *session, > + off_t file_offset, size_t sz, > + struct perf_record_aux *aux_event, > + struct perf_sample *sample) > +{ > + int err; > + char buf[PERF_SAMPLE_MAX_SIZE]; > + union perf_event *auxtrace_event_union; > + struct perf_record_auxtrace *auxtrace_event; > + union perf_event auxtrace_fragment; > + bool matchesCpuPid;
It's better to avoid using camel naming.
> + __u64 aux_offset; > + struct cs_etm_auxtrace *etm = container_of(session->auxtrace, > + struct cs_etm_auxtrace, > + auxtrace); > + > + /* > + * There should be a PERF_RECORD_AUXTRACE event at the file_offset that we got > + * from looping through the auxtrace index. > + */ > + err = perf_session__peek_event(session, file_offset, buf, > + PERF_SAMPLE_MAX_SIZE, &auxtrace_event_union, NULL); > + if (err) > + return err; > + auxtrace_event = &auxtrace_event_union->auxtrace; > + if (auxtrace_event->header.type != PERF_RECORD_AUXTRACE) > + return -EINVAL; > + > + if (auxtrace_event->header.size < sizeof(struct perf_record_auxtrace) || > + auxtrace_event->header.size != sz) { > + return -EINVAL; > + } > + > + /* > + * In per-thread mode, CPU is set to -1, but TID will be set instead. > + * See auxtrace_mmap_params__set_idx() > + */ > + if (auxtrace_event->cpu == (__u32) -1) > + matchesCpuPid = auxtrace_event->tid == sample->tid; > + else > + matchesCpuPid = auxtrace_event->cpu == sample->cpu;
If "matchesCpuPid" is false, can directly bail out at here, so can avoid the below unnecessary calculations.
> + > + /* > + * In snapshot/overwrite mode, the head points to the end of the buffer so aux_offset needs > + * to have the size subtracted so it points to the beginning as in normal mode. > + */ > + if (aux_event->flags & PERF_AUX_FLAG_OVERWRITE) > + aux_offset = aux_event->aux_offset - aux_event->aux_size; > + else > + aux_offset = aux_event->aux_offset; > + > + if (matchesCpuPid && > + aux_offset >= auxtrace_event->offset && > + aux_offset + aux_event->aux_size <= auxtrace_event->offset + auxtrace_event->size) {
It's possible that an event PERF_RECORD_AUXTRACE saves AUX trace data for multiple events PERF_RECORD_AUX (if we consider watermark).
So here the logic makes sense for me for checking the buffer range and I don't find any issue.
> + /* > + * If this AUX event was inside this buffer somewhere, create a new auxtrace event > + * based on the sizes of the aux event, and queue that fragment. > + */ > + auxtrace_fragment.auxtrace = *auxtrace_event; > + auxtrace_fragment.auxtrace.size = aux_event->aux_size; > + auxtrace_fragment.auxtrace.offset = aux_offset; > + file_offset += aux_offset - auxtrace_event->offset + auxtrace_event->header.size; > + return auxtrace_queues__add_event(&etm->queues, > + session, > + &auxtrace_fragment, > + file_offset, > + NULL); > + } > + > + /* Wasn't inside this buffer, but there were no parse errors. 1 == 'not found' */ > + return 1; > +} > + > +static int cs_etm__queue_aux_records_cb(struct perf_session *session, > + union perf_event *event, u64 offset __maybe_unused, > + void *data __maybe_unused) > +{ > + struct perf_sample sample; > + int ret; > + struct auxtrace_index_entry *ent; > + struct auxtrace_index *auxtrace_index; > + struct evsel *evsel; > + size_t i; > + struct cs_etm_auxtrace *etm = container_of(session->auxtrace, > + struct cs_etm_auxtrace, > + auxtrace); > + > + /* Don't care about any other events, we're only queuing buffers for AUX events */ > + if (event->header.type != PERF_RECORD_AUX) > + return 0; > + > + if (event->header.size < sizeof(struct perf_record_aux)) > + return -EINVAL; > + > + /* Truncated Aux records can have 0 size and shouldn't result in anything being queued. */ > + if (!event->aux.aux_size) > + return 0; > + > + /* > + * Parse the sample, we need the sample_id_all data that comes after the event so that the > + * CPU or PID can be matched to an AUXTRACE buffer's CPU or PID. > + */ > + evsel = evlist__event2evsel(session->evlist, event); > + evsel__parse_sample(evsel, event, &sample);
It's good to check the return errors from evsel__parse_sample().
> + > + /* > + * Loop throuch the auxtrace index to find the buffer that matches up with this > + * aux event. > + * TODO: binary search?
For binary search, you might need to reorg the auxtrace_index and its entries, I personally think this is not the priority.
> + */ > + list_for_each_entry(auxtrace_index, &session->auxtrace_index, list) { > + for (i = 0; i < auxtrace_index->nr; i++) { > + ent = &auxtrace_index->entries[i]; > + ret = cs_etm__queue_aux_fragment(session, ent->file_offset, > + ent->sz, &event->aux, &sample); > + if (!ret) { > + etm->data_queued = true; > + return 0; > + } else if (ret < 0) { > + /* > + * Anything other than 1 is an error. Positive values are 'not > + * found' we just want to go onto the next one in that case. > + */ > + return ret; > + } > + } > + }
It's good to add a warning at here? If cannot find a matched AUXRECORD event and fails to queue the fragment, it's likely caused by the AUX ring buffer's overrun.
> + > + /* > + * We would get here if there are no entries in the index (either no auxtrace buffers or > + * no index). Fail silently as there is the possibility of queueing them in > + * cs_etm__process_auxtrace_event() if etm->data_queued is still false; > + * > + * In that scenario, buffers will not be split by AUX records. > + */ > + return 0; > +} > + > +static int cs_etm__queue_aux_records(struct perf_session *session) > +{ > + return perf_session__peek_events(session, session->header.data_offset, > + session->header.data_size, > + cs_etm__queue_aux_records_cb, NULL); > +} > + > int cs_etm__process_auxtrace_info(union perf_event *event, > struct perf_session *session) > { > @@ -2879,12 +3034,10 @@ int cs_etm__process_auxtrace_info(union perf_event *event, > if (err) > goto err_delete_thread; > > - err = auxtrace_queues__process_index(&etm->queues, session); > + err = cs_etm__queue_aux_records(session); > if (err) > goto err_delete_thread; > > - etm->data_queued = etm->queues.populated;
Seems to me it's no reason to remove this sentence.
"etm->queues.populated" will be set when call auxtrace_queues__add_event(), so we still can assign it to "etm->data_queued" at here.
Thanks, Leo
> - > return 0; > > err_delete_thread: > -- > 2.28.0 >
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