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[68.147.0.187]) by smtp.gmail.com with ESMTPSA id d23sm244930pjz.15.2021.06.07.13.03.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 07 Jun 2021 13:03:24 -0700 (PDT) Date: Mon, 7 Jun 2021 14:03:21 -0600 From: Mathieu Poirier To: Leo Yan Cc: James Clark , acme@kernel.org, coresight@lists.linaro.org, al.grant@arm.com, branislav.rankov@arm.com, denik@chromium.org, suzuki.poulose@arm.com, anshuman.khandual@arm.com, Mike Leach , John Garry , Will Deacon , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , linux-arm-kernel@lists.infradead.org, linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v4 1/1] perf cs-etm: Split Coresight decode by aux records Message-ID: <20210607200321.GA179489@p14s> References: <20210601130751.25750-1-james.clark@arm.com> <20210601130751.25750-2-james.clark@arm.com> <20210604052117.GI10272@leoy-ThinkPad-X240s> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210604052117.GI10272@leoy-ThinkPad-X240s> Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org 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. > > > > 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. > > 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 > > --- > > 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 > >