[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
	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.