[lttng-modules.git] / README

LTTng 2.0 modules

Mathieu Desnoyers
July 19, 2011

LTTng 2.0 kernel modules build against a vanilla or distribution kernel, without
need for additional patches. Other features:

- 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 will need to have your kernel headers available (or
access to your full kernel source tree), and use:

% make
# make modules_install

If you need to specify the target directory to the kernel you want to build
against, use:

% KERNELDIR=path_to_kernel_dir make
# KERNELDIR=path_to_kernel_dir make modules_install

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 still in active development and not released yet.

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.
Commit	Line	Data
98541fcf MD	1	LTTng 2.0 modules
	2
	3	Mathieu Desnoyers
	4	July 19, 2011
	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)
fe178379	11	- Tracepoints, Function tracer, CPU Performance Monitoring Unit (PMU)
e5fb2910	12	counters, kprobes, and kretprobes support,
98541fcf MD	13	- Integrated interface for both kernel and userspace tracing,
98541fcf MD	14	- Have the ability to attach "context" information to events in the
fe178379 MD	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).
98541fcf MD	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
6b408629 MD	23	% make
6b408629 MD	24	# make modules_install
98541fcf MD	25
	26	If you need to specify the target directory to the kernel you want to build
	27	against, use:
	28
6b408629 MD	29	% KERNELDIR=path_to_kernel_dir make
6b408629 MD	30	# KERNELDIR=path_to_kernel_dir make modules_install
98541fcf	31
6b408629 MD	32	Use lttng-tools to control the tracer. LTTng tools should automatically load
	33	the kernel modules when needed. Use Babeltrace to print traces as a
	34	human-readable text log. These tools are available at the following URL:
	35	http://lttng.org/lttng2.0
bd2fc8af MD	36
	37	Please note that the LTTng-UST 2.0 (user-space tracing counterpart of LTTng 2.0)
	38	is still in active development and not released yet.
98541fcf	39
3da843ea MD	40	So far, it has been tested on vanilla Linux kernels 2.6.38, 2.6.39 and 3.0 (on
	41	x86 32/64-bit, and powerpc 32-bit at the moment, build tested on ARM). It should
	42	work fine with newer kernels and other architectures, but expect build issues
	43	with kernels older than 2.6.36. The clock source currently used is the standard
	44	gettimeofday (slower, less scalable and less precise than the LTTng 0.x clocks).
	45	Support for LTTng 0.x clocks will be added back soon into LTTng 2.0. Please
	46	note that lttng-modules 2.0 can build on a Linux kernel patched with the LTTng
	47	0.x patchset, but the lttng-modules 2.0 replace the lttng-modules 0.x, so both
c65998d6	48	tracers cannot be installed at the same time for a given kernel version.
a3a8ea22 MD	49
	50	* Note about Perf PMU counters support
	51
	52	Each PMU counter has its zero value set when it is attached to a context with
	53	add-context. Therefore, it is normal that the same counters attached to both the
	54	stream context and event context show different values for a given event; what
	55	matters is that they increment at the same rate.