perf test coresight: Add relevant documentation about ARM64 CoreSight testing

Add/improve documentation helping people get started with CoreSight and
perf as well as describe the testing and how it works.
Reviewed-by: James Clark <james.clark@arm.com>
Signed-off-by: Carsten Haitzler <carsten.haitzler@arm.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Suzuki Poulouse <suzuki.poulose@arm.com>
Cc: coresight@lists.linaro.org
Cc: linux-doc@vger.kernel.org
Link: https://lore.kernel.org/r/20220909152803.2317006-14-carsten.haitzler@foss.arm.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Documentation/trace/coresight/coresight-perf.rst

+.. 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.

tools/perf/Documentation/perf-arm-coresight.txt

+Arm CoreSight Support
+=====================
+
+For full documentation, see Documentation/trace/coresight/coresight-perf.rst
+in the kernel tree.