1 .. SPDX-License-Identifier: GPL-2.0
2
3 ================
4 CoreSight - Perf
5 ================
6
7 :Author: Carsten Haitzler <carsten.haitzler@arm.com>
8 :Date: June 29th, 2022
9
10 Perf is able to locally access CoreSight trace data and store it to the
11 output perf data files. This data can then be later decoded to give the
12 instructions that were traced for debugging or profiling purposes. You
13 can log such data with a perf record command like::
14
15 perf record -e cs_etm//u testbinary
16
17 This would run some test binary (testbinary) until it exits and record
18 a perf.data trace file. That file would have AUX sections if CoreSight
19 is working correctly. You can dump the content of this file as
20 readable text with a command like::
21
22 perf report --stdio --dump -i perf.data
23
24 You 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
40 If you see these above, then your system is tracing CoreSight data
41 correctly.
42
43 To compile perf with CoreSight support in the tools/perf directory do::
44
45 make CORESIGHT=1
46
47 This requires OpenCSD to build. You may install distribution packages
48 for the support such as libopencsd and libopencsd-dev or download it
49 and build yourself. Upstream OpenCSD is located at:
50
51 https://github.com/Linaro/OpenCSD
52
53 For complete information on building perf with CoreSight support and
54 more extensive usage look at:
55
56 https://github.com/Linaro/OpenCSD/blob/master/HOWTO.md
57
58
59 Kernel CoreSight Support
60 ------------------------
61
62 You will also want CoreSight support enabled in your kernel config.
63 Ensure it is enabled with::
64
65 CONFIG_CORESIGHT=y
66
67 There are various other CoreSight options you probably also want
68 enabled 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
79 Please refer to the kernel configuration help for more information.
80
81 Perf test - Verify kernel and userspace perf CoreSight work
82 -----------------------------------------------------------
83
84 When you run perf test, it will do a lot of self tests. Some of those
85 tests will cover CoreSight (only if enabled and on ARM64). You
86 generally would run perf test from the tools/perf directory in the
87 kernel 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
92 Some others will actually use perf record and some test binaries that
93 are in tests/shell/coresight and will collect traces to ensure a
94 minimum level of functionality is met. The scripts that launch these
95 tests 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
102 These perf record tests will not run if the tool binaries do not exist
103 in tests/shell/coresight/\*/ and will be skipped. If you do not have
104 CoreSight support in hardware then either do not build perf with
105 CoreSight support or remove these binaries in order to not have these
106 tests fail and have them skip instead.
107
108 These tests will log historical results in the current working
109 directory (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
115 These statistic files log some aspects of the AUX data sections in
116 the perf data output counting some numbers of certain encodings (a
117 good way to know that it's working in a very simple way). One problem
118 with CoreSight is that given a large enough amount of data needing to
119 be logged, some of it can be lost due to the processor not waking up
120 in time to read out all the data from buffers etc.. You will notice
121 that the amount of data collected can vary a lot per run of perf test.
122 If you wish to see how this changes over time, simply run perf test
123 multiple times and all these csv files will have more and more data
124 appended to it that you can later examine, graph and otherwise use to
125 figure out if things have become worse or better.
126
127 This means sometimes these tests fail as they don't capture all the
128 data needed. This is about tracking quality and amount of data
129 produced over time and to see when changes to the Linux kernel improve
130 quality of traces.
131
132 Be aware that some of these tests take quite a while to run, specifically
133 in processing the perf data file and dumping contents to then examine what
134 is inside.
135
136 You can change where these csv logs are stored by setting the
137 PERF_TEST_CORESIGHT_STATDIR environment variable before running perf
138 test like::
139
140 export PERF_TEST_CORESIGHT_STATDIR=/var/tmp
141 perf test
142
143 They will also store resulting perf output data in the current
144 directory for later inspection like::
145
146 perf-asm_pure_loop-out.data
147 perf-memcpy_thread-16k_10.data
148 ...
149
150 You can alter where the perf data files are stored by setting the
151 PERF_TEST_CORESIGHT_DATADIR environment variable such as::
152
153 PERF_TEST_CORESIGHT_DATADIR=/var/tmp
154 perf test
155
156 You may wish to set these above environment variables if you wish to
157 keep the output of tests outside of the current working directory for
158 longer term storage and examination.
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