Messages in this thread | | | Date | Tue, 8 Jun 2021 09:17:29 -0600 | From | Mathieu Poirier <> | Subject | Re: [RFC PATCH v4 1/1] perf cs-etm: Split Coresight decode by aux records |
| |
On Tue, Jun 08, 2021 at 05:28:08PM +0300, James Clark wrote: > > > On 07/06/2021 23:03, Mathieu Poirier wrote: > > Hi James, > > > > Leo has beat me to the punch on most of the things I noticed in this set, so > > this is just to complement what has already been pointed out. > > > > On Fri, Jun 04, 2021 at 01:21:17PM +0800, Leo Yan wrote: > >> 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. > > > > The first loop is enacted by perf_session__peek_events() and processes all the > > PERF_RECORD_AUX events. The second loop correlates PERF_RECORD_AUX with > > PERF_RECORD_AUXTRACE. > > > > The above paragraph seems to indicate the opposite. > > > > Hi Mathieu, > > Yes, you're right I will reword this. The rest of the comments I also agree > with so I will fix them up and submit v5. > > >>> > >>> 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. > > > > I would leave the idea of moving this to util/auxtrace.c alone for the time > > being. > > > >> > >>> 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. > > > > I think for the time being what you have here will work just fine. > > > >>> > >>> 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. > >>> > > > > I assume you did not expect this patch to be merged and as such wrote as much as > > you could, which is fine. The next revision should have a changelog that will > > concentrate on why this patch is needed. I think the testing section (below) is > > useful and should be kept around. > > Do you think something like this is enough for the reasoning: > > The reason that this change is needed is because AUX records are emitted > any time tracing is disabled, for example when the process is scheduled out. > Because ETM was disabled and enabled again, the decoder also needs to > be reset to force the search for a sync packet. Otherwise there would > be fatal decoding errors.
Yes, that will work. It describes _why_ this patch is needed.
> > Thanks > James > > > > >>> 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) > > > > The indentation doesn't work. The 'o' of off_t should be aligned with the 's' > > of struct on the first line. > > > >>> +{ > >>> + 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. > >> > > > > Leo is correct - I'm surprised checkpatch hasn't complained bitterly. > > > >>> + __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) > > > > Same comment about the indentation. > > > >>> +{ > >>> + 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); > >>> + > > struct cs_etm_auxtrace *etm = container_of(session->auxtrace, > > struct cs_etm_auxtrace, > > auxtrace); > > struct auxtrace_index *auxtrace_index; > > struct auxtrace_index_entry *ent; > > struct perf_sample sample; > > struct evsel *evsel; > > size_t i; > > int ret; > > > >>> + /* 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. > >> > > > > Here too I agree with Leo. > > > >>> + */ > >>> + 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); > > > > Perfect indentation. Here cs_etm__queue_aux_records() doesn't give us much. I > > would simply call perf_session__peek_events() from > > cs_etm__process_auxtrace_info(). > > > >>> +} > >>> + > >>> 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 > >> > > > > I'm happy with what is done in this patch. > > > > Thanks, > > Mathieu > > > >>> - > >>> return 0; > >>> > >>> err_delete_thread: > >>> -- > >>> 2.28.0 > >>>
| |