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| -rw-r--r-- | Documentation/trace/coresight/coresight-perf.rst | 158 |
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diff --git a/Documentation/trace/coresight/coresight-perf.rst b/Documentation/trace/coresight/coresight-perf.rst new file mode 100644 index 000000000000..d087aae7d492 --- /dev/null +++ b/Documentation/trace/coresight/coresight-perf.rst @@ -0,0 +1,158 @@ +.. SPDX-License-Identifier: GPL-2.0 + +================ +CoreSight - Perf +================ + + :Author: Carsten Haitzler <carsten.haitzler@arm.com> + :Date: June 29th, 2022 + +Perf is able to locally access CoreSight trace data and store it to the +output perf data files. This data can then be later decoded to give the +instructions that were traced for debugging or profiling purposes. You +can log such data with a perf record command like:: + + perf record -e cs_etm//u testbinary + +This would run some test binary (testbinary) until it exits and record +a perf.data trace file. That file would have AUX sections if CoreSight +is working correctly. You can dump the content of this file as +readable text with a command like:: + + perf report --stdio --dump -i perf.data + +You should find some sections of this file have AUX data blocks like:: + + 0x1e78 [0x30]: PERF_RECORD_AUXTRACE size: 0x11dd0 offset: 0 ref: 0x1b614fc1061b0ad1 idx: 0 tid: 531230 cpu: -1 + + . ... CoreSight ETM Trace data: size 73168 bytes + Idx:0; ID:10; I_ASYNC : Alignment Synchronisation. + Idx:12; ID:10; I_TRACE_INFO : Trace Info.; INFO=0x0 { CC.0 } + Idx:17; ID:10; I_ADDR_L_64IS0 : Address, Long, 64 bit, IS0.; Addr=0x0000000000000000; + Idx:26; ID:10; I_TRACE_ON : Trace On. + Idx:27; ID:10; I_ADDR_CTXT_L_64IS0 : Address & Context, Long, 64 bit, IS0.; Addr=0x0000FFFFB6069140; Ctxt: AArch64,EL0, NS; + Idx:38; ID:10; I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEEEEEEEEEEEEEE + Idx:39; ID:10; I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEEEEEEEEEEEEEE + Idx:40; ID:10; I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEEEEEEEEEEEEEE + Idx:41; ID:10; I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEN + ... + +If you see these above, then your system is tracing CoreSight data +correctly. + +To compile perf with CoreSight support in the tools/perf directory do:: + + make CORESIGHT=1 + +This requires OpenCSD to build. You may install distribution packages +for the support such as libopencsd and libopencsd-dev or download it +and build yourself. Upstream OpenCSD is located at: + + https://github.com/Linaro/OpenCSD + +For complete information on building perf with CoreSight support and +more extensive usage look at: + + https://github.com/Linaro/OpenCSD/blob/master/HOWTO.md + + +Kernel CoreSight Support +------------------------ + +You will also want CoreSight support enabled in your kernel config. +Ensure it is enabled with:: + + CONFIG_CORESIGHT=y + +There are various other CoreSight options you probably also want +enabled like:: + + CONFIG_CORESIGHT_LINKS_AND_SINKS=y + CONFIG_CORESIGHT_LINK_AND_SINK_TMC=y + CONFIG_CORESIGHT_CATU=y + CONFIG_CORESIGHT_SINK_TPIU=y + CONFIG_CORESIGHT_SINK_ETBV10=y + CONFIG_CORESIGHT_SOURCE_ETM4X=y + CONFIG_CORESIGHT_CTI=y + CONFIG_CORESIGHT_CTI_INTEGRATION_REGS=y + +Please refer to the kernel configuration help for more information. + +Perf test - Verify kernel and userspace perf CoreSight work +----------------------------------------------------------- + +When you run perf test, it will do a lot of self tests. Some of those +tests will cover CoreSight (only if enabled and on ARM64). You +generally would run perf test from the tools/perf directory in the +kernel tree. Some tests will check some internal perf support like: + + Check Arm CoreSight trace data recording and synthesized samples + Check Arm SPE trace data recording and synthesized samples + +Some others will actually use perf record and some test binaries that +are in tests/shell/coresight and will collect traces to ensure a +minimum level of functionality is met. The scripts that launch these +tests are in the same directory. These will all look like: + + CoreSight / ASM Pure Loop + CoreSight / Memcpy 16k 10 Threads + CoreSight / Thread Loop 10 Threads - Check TID + etc. + +These perf record tests will not run if the tool binaries do not exist +in tests/shell/coresight/\*/ and will be skipped. If you do not have +CoreSight support in hardware then either do not build perf with +CoreSight support or remove these binaries in order to not have these +tests fail and have them skip instead. + +These tests will log historical results in the current working +directory (e.g. tools/perf) and will be named stats-\*.csv like: + + stats-asm_pure_loop-out.csv + stats-memcpy_thread-16k_10.csv + ... + +These statistic files log some aspects of the AUX data sections in +the perf data output counting some numbers of certain encodings (a +good way to know that it's working in a very simple way). One problem +with CoreSight is that given a large enough amount of data needing to +be logged, some of it can be lost due to the processor not waking up +in time to read out all the data from buffers etc.. You will notice +that the amount of data collected can vary a lot per run of perf test. +If you wish to see how this changes over time, simply run perf test +multiple times and all these csv files will have more and more data +appended to it that you can later examine, graph and otherwise use to +figure out if things have become worse or better. + +This means sometimes these tests fail as they don't capture all the +data needed. This is about tracking quality and amount of data +produced over time and to see when changes to the Linux kernel improve +quality of traces. + +Be aware that some of these tests take quite a while to run, specifically +in processing the perf data file and dumping contents to then examine what +is inside. + +You can change where these csv logs are stored by setting the +PERF_TEST_CORESIGHT_STATDIR environment variable before running perf +test like:: + + export PERF_TEST_CORESIGHT_STATDIR=/var/tmp + perf test + +They will also store resulting perf output data in the current +directory for later inspection like:: + + perf-asm_pure_loop-out.data + perf-memcpy_thread-16k_10.data + ... + +You can alter where the perf data files are stored by setting the +PERF_TEST_CORESIGHT_DATADIR environment variable such as:: + + PERF_TEST_CORESIGHT_DATADIR=/var/tmp + perf test + +You may wish to set these above environment variables if you wish to +keep the output of tests outside of the current working directory for +longer term storage and examination. |