| 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 | |
| 6 | QUICKSTART |
| 7 | -------------- |
| 8 | |
| 9 | This is a quick start guide for the complete LTTng tool chain. This is divided |
| 10 | in three sections respectively kernel tracing, user-space tracing and reading a |
| 11 | trace. |
| 12 | |
| 13 | See the README file for installation procedure or use the various Linux |
| 14 | distribution packages. |
| 15 | |
| 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. |
| 20 | |
| 21 | lttng-tools provide a session daemon (lttng-sessiond) that acts as a tracing |
| 22 | registry. To trace any instrumented applications or the kernel, a registered |
| 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). |
| 25 | |
| 26 | Here is a list of some powerful features the LTTng 2.0 kernel tracer offers: |
| 27 | |
| 28 | * Kprobes support |
| 29 | * Function Tracer support |
| 30 | * Context information support (add context data to an event) |
| 31 | * Perf counter support |
| 32 | * Tracepoint support |
| 33 | |
| 34 | The next sections explain how to do tracing :) |
| 35 | |
| 36 | Kernel Tracing |
| 37 | -------------- |
| 38 | |
| 39 | You can start the session daemon by invoking the command "lttng-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. |
| 44 | |
| 45 | List available kernel events: |
| 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 | |
| 54 | If you have multiple sessions, you can change the current session by using |
| 55 | |
| 56 | # lttng set-session myothersession |
| 57 | |
| 58 | 2) Enable all tracepoints and all system call events. |
| 59 | |
| 60 | # lttng enable-event -a -k |
| 61 | |
| 62 | 3) Enable tracepoint event(s). Here for example, we want only |
| 63 | 'sched_switch' and 'sched_wakeup' events for the kernel (-k/--kernel). |
| 64 | |
| 65 | # lttng enable-event sched_switch,sched_wakeup -k |
| 66 | |
| 67 | or enable ALL tracepoint events: |
| 68 | |
| 69 | # lttng enable-event -a -k --tracepoint |
| 70 | |
| 71 | 4) Enable all system call event(s). |
| 72 | |
| 73 | # lttng enable-event -a -k --syscall |
| 74 | |
| 75 | 5) Enable kprobes and/or the function tracer with lttng |
| 76 | |
| 77 | This is a new feature made possible by the new LTTng 2.0 kernel tracer. You can |
| 78 | enable a dynamic probe and data will be output in the trace along side with |
| 79 | your tracing data. |
| 80 | |
| 81 | # lttng enable-event aname -k --probe symbol+0x0 |
| 82 | |
| 83 | or |
| 84 | |
| 85 | # lttng enable-event aname -k --probe 0xffff7260695 |
| 86 | |
| 87 | Either an <address> or a <symbol+offset> can be used for probes. |
| 88 | |
| 89 | You can also enable function tracer, which uses the Ftrace API (by Steven |
| 90 | Rostedt). Again, data will be output in the trace. |
| 91 | |
| 92 | # lttng enable-event aname -k --function <symbol_name> |
| 93 | |
| 94 | 6) Enable context information for an event: |
| 95 | |
| 96 | This is also a new feature which allows you to add context information to an |
| 97 | event. For example, you can add the PID along with the event information: |
| 98 | |
| 99 | # lttng add-context -k -e sched_switch -t pid |
| 100 | |
| 101 | At this point, you will have to look at 'lttng add-context --help' for all |
| 102 | possible context type which are integer values. |
| 103 | |
| 104 | You can on the same line activate multiple context: |
| 105 | |
| 106 | # lttng add-context -k -e sched_switch -t pid -t nice -t tid |
| 107 | |
| 108 | 7) Enable perf counter for an event: |
| 109 | |
| 110 | Again, a new powerful feature is the possibility to add perf counter data |
| 111 | (using the perf API by Ingo Molnar and Thomas Gleixner) to the trace on a per |
| 112 | event basis. Let say we want to get the CPU cycles at each event: |
| 113 | |
| 114 | # lttng add-context -k -e sched_switch -t perf:cpu-cycles |
| 115 | |
| 116 | You'll have to use the add-context help for all possible perf counter values. |
| 117 | |
| 118 | 8) Start tracing: |
| 119 | |
| 120 | # lttng start |
| 121 | |
| 122 | Tracing is in progress at this point and traces will be written in |
| 123 | $HOME/lttng-traces/mysession-<date>-<time> |
| 124 | |
| 125 | 9) Stop tracing: |
| 126 | |
| 127 | # lttng stop |
| 128 | |
| 129 | Note: At this point, you can restart the trace (lttng start), enable/disable |
| 130 | events or just go take a break and come back 3 days later to start it again :). |
| 131 | |
| 132 | 10) Destroy your session after you are done with tracing |
| 133 | |
| 134 | # lttng destroy |
| 135 | |
| 136 | See Reading a trace section below to read you trace(s). |
| 137 | |
| 138 | User-space Tracing |
| 139 | -------------- |
| 140 | |
| 141 | User-space tracer 2.0 not released at this point. For the 0.x versions, |
| 142 | you need to use 'ustctl' to control user-space tracing. |
| 143 | |
| 144 | Reading a trace |
| 145 | -------------- |
| 146 | |
| 147 | The tool "Babeltrace" can be used to dump your binary trace into a |
| 148 | human-readable text format. Please see |
| 149 | http://www.efficios.com/babeltrace and git tree |
| 150 | http://git.efficios.com/?p=babeltrace.git |
| 151 | |
| 152 | # babeltrace $HOME/lttng-traces/mysession-<date>-<time> | less |
| 153 | |
| 154 | VoilĂ ! |
| 155 | |
| 156 | Please report any bugs/comments on our mailing list |
| 157 | (ltt-dev@lists.casi.polymtl.ca) or you can go on our IRC channel at |
| 158 | irc.oftc.net, channel #lttng |