Populate the auxtrace queues using AUX records rather than whole
auxtrace buffers so that the decoder is reset between each aux record.
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.
But now we loop over all PERF_RECORD_AUX events instead of AUXTRACE
buffers. For each PERF_RECORD_AUX event, we find the corresponding
AUXTRACE buffer using the index, and add a fragment of that buffer to
the auxtrace queues.
No other changes to decoding were made, apart from populating the
auxtrace queues. The result of decoding is identical to before, except
in cases where decoding failed completely, due to not resetting the
decoder.
The reason for this change 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.
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 (various files with and without buffer wrap)
perf record -e cs_etm/@tmc_etr0/u -a --snapshot
Some differences were observed in the following scenario:
* Snapshot mode (with duplicate buffers)
perf record -e cs_etm/@tmc_etr0/u -a --snapshot
Fewer samples are generated in snapshot mode if duplicate buffers
were gathered because buffers with the same offset are now only added
once. This gives different, but more correct results and no duplicate
data is decoded any more.
Signed-off-by: James Clark <james.clark@arm.com>
Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Tested-by: Leo Yan <leo.yan@linaro.org>
Cc: Al Grant <al.grant@arm.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Branislav Rankov <branislav.rankov@arm.com>
Cc: Denis Nikitin <denik@chromium.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: John Garry <john.garry@huawei.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lore.kernel.org/lkml/20210624164303.28632-2-james.clark@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
83d1fc92d4