Date:   Wed, 10 Aug 2022 18:59:07 +0100
From:   Carsten Haitzler <carsten.haitzler@...s.arm.com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     linux-kernel@...r.kernel.org, coresight@...ts.linaro.org,
        suzuki.poulose@....com, mathieu.poirier@...aro.org,
        mike.leach@...aro.org, linux-perf-users@...r.kernel.org,
        acme@...nel.org
Subject: Re: [PATCH v5 14/14] perf test: Add relevant documentation about
 CoreSight testing



On 8/7/22 08:03, Leo Yan wrote:
> On Thu, Jul 28, 2022 at 03:52:56PM +0100, carsten.haitzler@...s.arm.com wrote:
>> From: "Carsten Haitzler (Rasterman)" <raster@...terman.com>
>>
>> Add/improve documentation helping people get started with CoreSight and
>> perf as well as describe the testing and how it works.
>>
>> Cc: linux-doc@...r.kernel.org
>> Signed-off-by: Carsten Haitzler <carsten.haitzler@....com>
>> ---
>>   .../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@....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_STM=y
>> +   CONFIG_CORESIGHT_CPU_DEBUG=y
> 
> So far CORESIGHT_STM and CORESIGHT_CPU_DEBUG are irrelevant with perf
> recording.  Perf only creates path from source (ETM) to sink (TMC-ETR
> or TMC-ETF), so it's good to drop them.

will do.

>> +   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 whish to
> 
> s/whish/wish/

good catch. :)

>> +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
> 
> You could see we have a document perf-arm-spe.txt, for alignment it's
> good to rename this file as perf-arm-coresight.txt.
> 
> The rest of this patch is good for me, with addressing the above minor
> comments:

will do.

> Reviewed-by: Leo Yan <leo.yan@...aro.org>
> 
> 
>> @@ -0,0 +1,5 @@
>> +Arm CoreSight Support
>> +=====================
>> +
>> +For full documentation, see Documentation/trace/coresight/coresight-perf.rst
>> +in the kernel tree.
>> -- 
>> 2.32.0
>>

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