README.md

   1 LTTng-modules
   2 =============
   3
   4 _by [Mathieu Desnoyers](mailto:mathieu.desnoyers@efficios.com)_
   5
   6
   7 LTTng kernel modules are Linux kernel modules which make
   8 [LTTng](http://lttng.org/) kernel tracing possible. They include
   9 essential control modules and many probes which instrument numerous
  10 interesting parts of Linux. LTTng-modules builds against a vanilla or
  11 distribution kernel, with no need for additional patches.
  12
  13 Other notable features:
  14
  15   - Produces [CTF](http://www.efficios.com/ctf)
  16     (Common Trace Format) natively,
  17   - Tracepoints, function tracer, CPU Performance Monitoring Unit (PMU)
  18     counters, kprobes, and kretprobes support,
  19   - Have the ability to attach _context_ information to events in the
  20     trace (e.g., any PMU counter, PID, PPID, TID, command name, etc).
  21     All the extra information fields to be collected with events are
  22     optional, specified on a per-tracing-session basis (except for
  23     timestamp and event ID, which are mandatory).
  24
  25
  26 Building
  27 --------
  28
  29 To build and install LTTng-modules, you will need to have your kernel
  30 headers available (or access to your full kernel source tree), and do:
  31
  32     make
  33     sudo make modules_install
  34     sudo depmod -a
  35
  36 The above commands will build LTTng-modules against your
  37 current kernel. If you need to build LTTng-modules against a custom
  38 kernel, do:
  39
  40     make KERNELDIR=/path/to/custom/kernel
  41     sudo make KERNELDIR=/path/to/custom/kernel modules_install
  42     sudo depmod -a kernel_version
  43
  44
  45 ### Kernel built-in support
  46
  47 It is also possible to build these modules as part of a kernel image. Simply
  48 run the [`scripts/built-in.sh`](scripts/built-in.sh) script with the path to
  49 your kernel source directory as an argument.  It will symlink the
  50 lttng-modules directory in the kernel sources and add an include in the kernel
  51 Makefile.
  52
  53 Then configure your kernel as usual and enable the `CONFIG_LTTNG` option.
  54
  55
  56 ### Required kernel config options
  57
  58 Make sure your target kernel has the following config options enabled:
  59
  60   - `CONFIG_MODULES`: loadable module support (not strictly required
  61      when built into the kernel),
  62   - `CONFIG_HIGH_RES_TIMERS`: needed for LTTng 2.x clock source,
  63   - `CONFIG_TRACEPOINTS`: kernel tracepoint instrumentation
  64      (enabled as a side-effect of any of the perf/ftrace/blktrace
  65      instrumentation features).
  66
  67
  68 ### Supported (optional) kernel config options
  69
  70 The following kernel configuration options will affect the features
  71 available from LTTng:
  72
  73   - `CONFIG_HAVE_SYSCALL_TRACEPOINTS`: system call tracing:
  74
  75         lttng enable-event -k --syscall
  76         lttng enable-event -k -a
  77
  78   - `CONFIG_PERF_EVENTS`: performance counters:
  79
  80         lttng add-context -t perf:*
  81
  82   - `CONFIG_EVENT_TRACING`: needed to allow block layer tracing
  83   - `CONFIG_KPROBES`: dynamic probes:
  84
  85         lttng enable-event -k --probe ...
  86
  87   - `CONFIG_KRETPROBES`: dynamic function entry/return probes:
  88
  89         lttng enable-event -k --function ...
  90
  91 Customization/Extension
  92 -----------------------
  93
  94 The lttng-modules source includes definitions for the actual callback
  95 functions that will be attached to the kernel tracepoints by lttng.
  96 The lttng-modules project implements its own macros generating these
  97 callbacks: the LTTNG_TRACEPOINT_EVENT macro family found in
  98 instrumentation/events/lttng-module/. In order to show up in a
  99 lttng-modules trace, a kernel tracepoint must be defined within the
 100 kernel tree, and also defined within lttng-modules with the
 101 LTTNG_TRACEPOINT_EVENT macro family. Customizations or extensions must
 102 be done by modifying instances of these macros within the lttng-modules
 103 source.
 104
 105 Usage
 106 -----
 107
 108 Use [LTTng-tools](https://lttng.org/download) to control the tracer.
 109 The session daemon of LTTng-tools should automatically load the LTTng
 110 kernel modules when needed. Use [Babeltrace](https://lttng.org/babeltrace)
 111 to print traces as a human-readable text log.
 112
 113
 114 Support
 115 -------
 116
 117 Linux kernels >= 3.0 are supported.
 118
 119
 120 Notes
 121 -----
 122
 123 ### About perf PMU counters support
 124
 125 Each PMU counter has its zero value set when it is attached to a context with
 126 add-context. Therefore, it is normal that the same counters attached to both the
 127 stream context and event context show different values for a given event; what
 128 matters is that they increment at the same rate.