[PATCH 14/14] perf test: Add relevant documentation about CoreSight testing

From: carsten . haitzler
Date: Tue Jul 12 2022 - 09:59:27 EST

From: "Carsten Haitzler (Rasterman)" <raster@xxxxxxxxxxxxx>

Add/improve documentation helping people get started with CoreSight and
perf as well as describe the testing and how it works.

Cc: linux-doc@xxxxxxxxxxxxxxx
Signed-off-by: Carsten Haitzler <carsten.haitzler@xxxxxxx>
.../trace/coresight/coresight-perf.rst | 160 ++++++++++++++++++
tools/perf/Documentation/arm-coresight.txt | 5 +
2 files changed, 165 insertions(+)
create mode 100644 Documentation/trace/coresight/coresight-perf.rst
create mode 100644 tools/perf/Documentation/arm-coresight.txt

diff --git a/Documentation/trace/coresight/coresight-perf.rst b/Documentation/trace/coresight/coresight-perf.rst
new file mode 100644
index 000000000000..401a097aea4b
--- /dev/null
+++ b/Documentation/trace/coresight/coresight-perf.rst
@@ -0,0 +1,160 @@
+.. SPDX-License-Identifier: GPL-2.0
+CoreSight - Perf
+ :Author: Carsten Haitzler <carsten.haitzler@xxxxxxx>
+ :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
+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::
+There are various other CoreSight options you probably also want
+enabled like::
+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::
+ 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
+You may wish to set these above environment variables if you whish to
+keep the output of tests outside of the current working directory for
+longer term storage and examination.
diff --git a/tools/perf/Documentation/arm-coresight.txt b/tools/perf/Documentation/arm-coresight.txt
new file mode 100644
index 000000000000..c117fc50a2a9
--- /dev/null
+++ b/tools/perf/Documentation/arm-coresight.txt
@@ -0,0 +1,5 @@
+Arm CoreSight Support
+For full documentation, see Documentation/trace/coresight/coresight-perf.rst
+in the kernel tree.