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1 | NOTES: |
2 | -------------- | |
3 | 2011-07-21 : User-space tracer is not released. Tracing in user-space at this | |
4 | point is not possible with lttng-tools. | |
5 | ||
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6 | QUICKSTART |
7 | -------------- | |
8 | ||
9 | This is a quick start guide for the complete LTTng tool chain. This is divided | |
6f8eb304 | 10 | in three sections respectively kernel tracing, user-space tracing and reading a |
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11 | trace. |
12 | ||
13 | See the README file for installation procedure or use the various Linux | |
14 | distribution packages. | |
15 | ||
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16 | In order to trace the kernel, you'll need the lttng-modules >= 2.0 compiled and |
17 | installed. See http://lttng.org/lttng2.0 for more instructions for that part. | |
18 | For user-space tracing, you'll need an instrumented application, please see | |
19 | http://lttng.org/ust. | |
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20 | |
21 | lttng-tools provide a session daemon (ltt-sessiond) that acts as a tracing | |
22 | registry. To trace any instrumented applications or the kernel, a registered | |
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23 | tracing session is needed beforehand. To interact with the session daemon and a |
24 | tracing session, you should use the lttng command line UI (lttng). | |
e7651054 | 25 | |
617d7d15 | 26 | Here is a list of some powerful features the LTTng 2.0 kernel tracer offers: |
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27 | |
28 | * Kprobes support | |
29 | * Function Tracer support | |
30 | * Context information support (add context data to an event) | |
31 | * Perf counter support | |
617d7d15 | 32 | * Tracepoint support |
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33 | |
34 | The next sections explain how to do tracing :) | |
35 | ||
36 | Kernel Tracing | |
37 | -------------- | |
38 | ||
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39 | You can start the session daemon by invoking the command "ltt-sessiond", |
40 | or let the lttng command line tool do it for you. The session daemon | |
41 | loads the LTTng tracer modules for you if those modules can be found on | |
42 | your system. If they are not found, the kernel tracing feature will be | |
43 | unavailable. | |
e7651054 | 44 | |
495c67f5 | 45 | List available kernel events: |
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46 | |
47 | # lttng list -k | |
48 | ||
49 | 1) Create a tracing session. A .lttngrc will be created in $HOME containing | |
50 | the session name (here 'mysession') you are working on. | |
51 | ||
52 | # lttng create mysession | |
53 | ||
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54 | If you have multiple sessions, you can change the current session by using |
55 | ||
56 | # lttng set-session myothersession | |
57 | ||
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58 | 2) Enable event(s). Here for example, we want only 'sched_switch' and |
59 | 'sys_enter' events for the kernel (-k/--kernel). | |
60 | ||
61 | # lttng enable-event sched_switch,sys_enter -k | |
62 | ||
63 | or enable ALL events (-a/--all): | |
64 | ||
65 | # lttng enable-event -a -k | |
66 | ||
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67 | 3) Enable kprobes and/or the function tracer with lttng |
68 | ||
69 | This is a new feature made possible by the new LTTng 2.0 kernel tracer. You can | |
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70 | enable a dynamic probe and data will be output in the trace along side with |
71 | your tracing data. | |
6f8eb304 | 72 | |
975fdf53 | 73 | # lttng enable-event aname -k --probe symbol+0xffff7260695 |
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74 | |
75 | or | |
76 | ||
975fdf53 | 77 | # lttng enable-event aname -k --probe 0xffff7260695 |
6f8eb304 | 78 | |
617d7d15 | 79 | Either an <address> or a <symbol+offset> can be used for probes. |
6f8eb304 | 80 | |
617d7d15 | 81 | You can also enable function tracer, which uses the Ftrace API (by Steven |
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82 | Rostedt). Again, data will be output in the trace. |
83 | ||
975fdf53 | 84 | # lttng enable-event aname -k --function <symbol_name> |
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85 | |
86 | 4) Enable context information for an event: | |
87 | ||
88 | This is also a new feature which allows you to add context information to an | |
89 | event. For example, you can add the PID along with the event information: | |
90 | ||
617d7d15 | 91 | # lttng add-context -k -e sched_switch -t pid |
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92 | |
93 | At this point, you will have to look at 'lttng add-context --help' for all | |
94 | possible context type which are integer values. | |
95 | ||
96 | You can on the same line activate multiple context: | |
97 | ||
617d7d15 | 98 | # lttng add-context -k -e sched_switch -t pid -t nice -t tid |
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99 | |
100 | 5) Enable perf counter for an event: | |
101 | ||
102 | Again, a new powerful feature is the possibility to add perf counter data | |
90b9a268 | 103 | (using the perf API by Ingo Molnar and Thomas Gleixner) to the trace on a per |
617d7d15 | 104 | event basis. Let say we want to get the CPU cycles at each event: |
6f8eb304 | 105 | |
617d7d15 | 106 | # lttng add-context -k -e sched_switch -t perf:cpu-cycles |
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107 | |
108 | You'll have to use the add-context help for all possible perf counter values. | |
109 | ||
110 | 6) Start tracing: | |
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111 | |
112 | # lttng start | |
113 | ||
6f8eb304 | 114 | Tracing is in progress at this point and traces will be written in |
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115 | $HOME/lttng-traces/mysession-<date>-<time> |
116 | ||
6f8eb304 | 117 | 7) Stop tracing: |
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118 | |
119 | # lttng stop | |
120 | ||
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121 | Note: At this point, you can restart the trace (lttng start), enable/disable |
122 | events or just go take a break and come back 3 days later to start it again :). | |
123 | ||
124 | 8) Destroy your session after you are done with tracing | |
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125 | |
126 | # lttng destroy | |
127 | ||
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128 | See Reading a trace section below to read you trace(s). |
129 | ||
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130 | User-space Tracing |
131 | -------------- | |
132 | ||
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133 | User-space tracer 2.0 not released at this point. For the 0.x versions, |
134 | you need to use 'ustctl' to control user-space tracing. | |
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135 | |
136 | Reading a trace | |
137 | -------------- | |
138 | ||
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139 | The tool "Babeltrace" can be used to dump your binary trace into a |
140 | human-readable text format. Please see | |
141 | http://www.efficios.com/babeltrace and git tree | |
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142 | http://git.efficios.com/?p=babeltrace.git |
143 | ||
144 | # babeltrace -n $HOME/lttng-traces/mysession-<date>-<time> | less | |
145 | ||
146 | VoilĂ ! | |
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147 | |
148 | Please report any bugs/comments on our mailing list | |
149 | (ltt-dev@lists.casi.polymtl.ca) or you can go on our IRC channel at | |
150 | irc.oftc.net, channel #lttng |