[lttng-modules.git] / README

LTTng 2.0 modules

Mathieu Desnoyers
February 8, 2012

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
# depmod -a

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
# depmod -a kernel_version

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

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.

LTTng-modules depends on having kallsyms enabled in the kernel it is
built against. Ideally, if you want to have system call tracing, the
"Trace Syscalls" feature should be enabled too. 

* 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
936e4abc	4	February 8, 2012
98541fcf MD	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
65a8ae6b	25	# depmod -a
98541fcf MD	26
	27	If you need to specify the target directory to the kernel you want to build
	28	against, use:
	29
6b408629 MD	30	% KERNELDIR=path_to_kernel_dir make
6b408629 MD	31	# KERNELDIR=path_to_kernel_dir make modules_install
65a8ae6b	32	# depmod -a kernel_version
98541fcf	33
6b408629 MD	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
bd2fc8af	38
3da843ea MD	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
c65998d6	47	tracers cannot be installed at the same time for a given kernel version.
a3a8ea22	48
936e4abc MD	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
a3a8ea22 MD	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.