1.. SPDX-License-Identifier: GPL-2.0
2
3================
4CoreSight - Perf
5================
6
7    :Author:   Carsten Haitzler <carsten.haitzler@arm.com>
8    :Date:     June 29th, 2022
9
10Perf is able to locally access CoreSight trace data and store it to the
11output perf data files. This data can then be later decoded to give the
12instructions that were traced for debugging or profiling purposes. You
13can log such data with a perf record command like::
14
15   perf record -e cs_etm//u testbinary
16
17This would run some test binary (testbinary) until it exits and record
18a perf.data trace file. That file would have AUX sections if CoreSight
19is working correctly. You can dump the content of this file as
20readable text with a command like::
21
22   perf report --stdio --dump -i perf.data
23
24You should find some sections of this file have AUX data blocks like::
25
26   0x1e78 [0x30]: PERF_RECORD_AUXTRACE size: 0x11dd0  offset: 0  ref: 0x1b614fc1061b0ad1  idx: 0  tid: 531230  cpu: -1
27
28   . ... CoreSight ETM Trace data: size 73168 bytes
29           Idx:0; ID:10;   I_ASYNC : Alignment Synchronisation.
30             Idx:12; ID:10;  I_TRACE_INFO : Trace Info.; INFO=0x0 { CC.0 }
31             Idx:17; ID:10;  I_ADDR_L_64IS0 : Address, Long, 64 bit, IS0.; Addr=0x0000000000000000;
32             Idx:26; ID:10;  I_TRACE_ON : Trace On.
33             Idx:27; ID:10;  I_ADDR_CTXT_L_64IS0 : Address & Context, Long, 64 bit, IS0.; Addr=0x0000FFFFB6069140; Ctxt: AArch64,EL0, NS;
34             Idx:38; ID:10;  I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEEEEEEEEEEEEEE
35             Idx:39; ID:10;  I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEEEEEEEEEEEEEE
36             Idx:40; ID:10;  I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEEEEEEEEEEEEEE
37             Idx:41; ID:10;  I_ATOM_F6 : Atom format 6.; EEEEEEEEEEEN
38             ...
39
40If you see these above, then your system is tracing CoreSight data
41correctly.
42
43To compile perf with CoreSight support in the tools/perf directory do::
44
45    make CORESIGHT=1
46
47This requires OpenCSD to build. You may install distribution packages
48for the support such as libopencsd and libopencsd-dev or download it
49and build yourself. Upstream OpenCSD is located at:
50
51  https://github.com/Linaro/OpenCSD
52
53For complete information on building perf with CoreSight support and
54more extensive usage look at:
55
56  https://github.com/Linaro/OpenCSD/blob/master/HOWTO.md
57
58
59Kernel CoreSight Support
60------------------------
61
62You will also want CoreSight support enabled in your kernel config.
63Ensure it is enabled with::
64
65   CONFIG_CORESIGHT=y
66
67There are various other CoreSight options you probably also want
68enabled like::
69
70   CONFIG_CORESIGHT_LINKS_AND_SINKS=y
71   CONFIG_CORESIGHT_LINK_AND_SINK_TMC=y
72   CONFIG_CORESIGHT_CATU=y
73   CONFIG_CORESIGHT_SINK_TPIU=y
74   CONFIG_CORESIGHT_SINK_ETBV10=y
75   CONFIG_CORESIGHT_SOURCE_ETM4X=y
76   CONFIG_CORESIGHT_CTI=y
77   CONFIG_CORESIGHT_CTI_INTEGRATION_REGS=y
78
79Please refer to the kernel configuration help for more information.
80
81Perf test - Verify kernel and userspace perf CoreSight work
82-----------------------------------------------------------
83
84When you run perf test, it will do a lot of self tests. Some of those
85tests will cover CoreSight (only if enabled and on ARM64). You
86generally would run perf test from the tools/perf directory in the
87kernel tree. Some tests will check some internal perf support like:
88
89   Check Arm CoreSight trace data recording and synthesized samples
90   Check Arm SPE trace data recording and synthesized samples
91
92Some others will actually use perf record and some test binaries that
93are in tests/shell/coresight and will collect traces to ensure a
94minimum level of functionality is met. The scripts that launch these
95tests are in the same directory. These will all look like:
96
97   CoreSight / ASM Pure Loop
98   CoreSight / Memcpy 16k 10 Threads
99   CoreSight / Thread Loop 10 Threads - Check TID
100   etc.
101
102These perf record tests will not run if the tool binaries do not exist
103in tests/shell/coresight/\*/ and will be skipped. If you do not have
104CoreSight support in hardware then either do not build perf with
105CoreSight support or remove these binaries in order to not have these
106tests fail and have them skip instead.
107
108These tests will log historical results in the current working
109directory (e.g. tools/perf) and will be named stats-\*.csv like:
110
111   stats-asm_pure_loop-out.csv
112   stats-memcpy_thread-16k_10.csv
113   ...
114
115These statistic files log some aspects of the AUX data sections in
116the perf data output counting some numbers of certain encodings (a
117good way to know that it's working in a very simple way). One problem
118with CoreSight is that given a large enough amount of data needing to
119be logged, some of it can be lost due to the processor not waking up
120in time to read out all the data from buffers etc.. You will notice
121that the amount of data collected can vary a lot per run of perf test.
122If you wish to see how this changes over time, simply run perf test
123multiple times and all these csv files will have more and more data
124appended to it that you can later examine, graph and otherwise use to
125figure out if things have become worse or better.
126
127This means sometimes these tests fail as they don't capture all the
128data needed. This is about tracking quality and amount of data
129produced over time and to see when changes to the Linux kernel improve
130quality of traces.
131
132Be aware that some of these tests take quite a while to run, specifically
133in processing the perf data file and dumping contents to then examine what
134is inside.
135
136You can change where these csv logs are stored by setting the
137PERF_TEST_CORESIGHT_STATDIR environment variable before running perf
138test like::
139
140   export PERF_TEST_CORESIGHT_STATDIR=/var/tmp
141   perf test
142
143They will also store resulting perf output data in the current
144directory for later inspection like::
145
146   perf-asm_pure_loop-out.data
147   perf-memcpy_thread-16k_10.data
148   ...
149
150You can alter where the perf data files are stored by setting the
151PERF_TEST_CORESIGHT_DATADIR environment variable such as::
152
153   PERF_TEST_CORESIGHT_DATADIR=/var/tmp
154   perf test
155
156You may wish to set these above environment variables if you wish to
157keep the output of tests outside of the current working directory for
158longer term storage and examination.
159