drivers/staging/lttng/README

LTTng 2.0 modules

Mathieu Desnoyers
November 1st, 2011

LTTng 2.0 kernel modules is currently part of the Linux kernel staging
tree. It features (new features since LTTng 0.x):

- Produces CTF (Common Trace Format) natively,
  (http://www.efficios.com/ctf)
- Tracepoints, Function tracer, CPU Performance Monitoring Unit (PMU)
  counters, kprobes, and kretprobes support,
- Integrated interface for both kernel and userspace tracing,
- Have the ability to attach "context" information to events in the
  trace (e.g. any PMU counter, pid, ppid, tid, comm name, etc).
  All the extra information fields to be collected with events are
  optional, specified on a per-tracing-session basis (except for
  timestamp and event id, which are mandatory).

To build and install, you need to select "Staging" modules, and the
LTTng kernel tracer.

Use lttng-tools to control the tracer. LTTng tools should automatically
load the kernel modules when needed. Use Babeltrace to print traces as a
human-readable text log. These tools are available at the following URL:
http://lttng.org/lttng2.0

Please note that the LTTng-UST 2.0 (user-space tracing counterpart of
LTTng 2.0) is now ready to be used, but still only available from the
git repository.

So far, it has been tested on vanilla Linux kernels 2.6.38, 2.6.39 and
3.0 (on x86 32/64-bit, and powerpc 32-bit at the moment, build tested on
ARM). It should work fine with newer kernels and other architectures,
but expect build issues with kernels older than 2.6.36. The clock source
currently used is the standard gettimeofday (slower, less scalable and
less precise than the LTTng 0.x clocks).  Support for LTTng 0.x clocks
will be added back soon into LTTng 2.0.  Please note that lttng-modules
2.0 can build on a Linux kernel patched with the LTTng 0.x patchset, but
the lttng-modules 2.0 replace the lttng-modules 0.x, so both tracers
cannot be installed at the same time for a given kernel version.

* Note about Perf PMU counters support

Each PMU counter has its zero value set when it is attached to a context with
add-context. Therefore, it is normal that the same counters attached to both the
stream context and event context show different values for a given event; what
matters is that they increment at the same rate.