README

   1 LTTng 2.0 modules
   2
   3 Mathieu Desnoyers
   4 February 8, 2012
   5
   6 LTTng 2.0 kernel modules build against a vanilla or distribution kernel, without
   7 need for additional patches. Other features:
   8
   9 - Produces CTF (Common Trace Format) natively,
  10   (http://www.efficios.com/ctf)
  11 - Tracepoints, Function tracer, CPU Performance Monitoring Unit (PMU)
  12   counters, kprobes, and kretprobes support,
  13 - Integrated interface for both kernel and userspace tracing,
  14 - Have the ability to attach "context" information to events in the
  15   trace (e.g. any PMU counter, pid, ppid, tid, comm name, etc).
  16   All the extra information fields to be collected with events are
  17   optional, specified on a per-tracing-session basis (except for
  18   timestamp and event id, which are mandatory).
  19
  20 To build and install, you will need to have your kernel headers available (or
  21 access to your full kernel source tree), and use:
  22
  23 % make
  24 # make modules_install
  25 # depmod -a
  26
  27 If you need to specify the target directory to the kernel you want to build
  28 against, use:
  29
  30 % KERNELDIR=path_to_kernel_dir make
  31 # KERNELDIR=path_to_kernel_dir make modules_install
  32 # depmod -a kernel_version
  33
  34 Use lttng-tools to control the tracer. LTTng tools should automatically load
  35 the kernel modules when needed. Use Babeltrace to print traces as a
  36 human-readable text log. These tools are available at the following URL:
  37 http://lttng.org/lttng2.0
  38
  39 So far, it has been tested on vanilla Linux kernels 2.6.38, 2.6.39 and 3.0 (on
  40 x86 32/64-bit, and powerpc 32-bit at the moment, build tested on ARM). It should
  41 work fine with newer kernels and other architectures, but expect build issues
  42 with kernels older than 2.6.36. The clock source currently used is the standard
  43 gettimeofday (slower, less scalable and less precise than the LTTng 0.x clocks).
  44 Support for LTTng 0.x clocks will be added back soon into LTTng 2.0.  Please
  45 note that lttng-modules 2.0 can build on a Linux kernel patched with the LTTng
  46 0.x patchset, but the lttng-modules 2.0 replace the lttng-modules 0.x, so both
  47 tracers cannot be installed at the same time for a given kernel version.
  48
  49 LTTng-modules depends on having kallsyms enabled in the kernel it is
  50 built against. Ideally, if you want to have system call tracing, the
  51 "Trace Syscalls" feature should be enabled too.
  52
  53 * Note about Perf PMU counters support
  54
  55 Each PMU counter has its zero value set when it is attached to a context with
  56 add-context. Therefore, it is normal that the same counters attached to both the
  57 stream context and event context show different values for a given event; what
  58 matters is that they increment at the same rate.