52ad51e7a9
We need common default directory of denbugfs for consistency. (debugfs's default directory is /sys/kernel/debug/ by debugfs.) Signed-off-by: GeunSik Lim <geunsik.lim@samsung.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
100 lines
2.9 KiB
Plaintext
100 lines
2.9 KiB
Plaintext
Event Tracing
|
|
|
|
Documentation written by Theodore Ts'o
|
|
Updated by Li Zefan
|
|
|
|
1. Introduction
|
|
===============
|
|
|
|
Tracepoints (see Documentation/trace/tracepoints.txt) can be used
|
|
without creating custom kernel modules to register probe functions
|
|
using the event tracing infrastructure.
|
|
|
|
Not all tracepoints can be traced using the event tracing system;
|
|
the kernel developer must provide code snippets which define how the
|
|
tracing information is saved into the tracing buffer, and how the
|
|
tracing information should be printed.
|
|
|
|
2. Using Event Tracing
|
|
======================
|
|
|
|
2.1 Via the 'set_event' interface
|
|
---------------------------------
|
|
|
|
The events which are available for tracing can be found in the file
|
|
/sys/kernel/debug/tracing/available_events.
|
|
|
|
To enable a particular event, such as 'sched_wakeup', simply echo it
|
|
to /sys/kernel/debug/tracing/set_event. For example:
|
|
|
|
# echo sched_wakeup >> /sys/kernel/debug/tracing/set_event
|
|
|
|
[ Note: '>>' is necessary, otherwise it will firstly disable
|
|
all the events. ]
|
|
|
|
To disable an event, echo the event name to the set_event file prefixed
|
|
with an exclamation point:
|
|
|
|
# echo '!sched_wakeup' >> /sys/kernel/debug/tracing/set_event
|
|
|
|
To disable all events, echo an empty line to the set_event file:
|
|
|
|
# echo > /sys/kernel/debug/tracing/set_event
|
|
|
|
To enable all events, echo '*:*' or '*:' to the set_event file:
|
|
|
|
# echo *:* > /sys/kernel/debug/tracing/set_event
|
|
|
|
The events are organized into subsystems, such as ext4, irq, sched,
|
|
etc., and a full event name looks like this: <subsystem>:<event>. The
|
|
subsystem name is optional, but it is displayed in the available_events
|
|
file. All of the events in a subsystem can be specified via the syntax
|
|
"<subsystem>:*"; for example, to enable all irq events, you can use the
|
|
command:
|
|
|
|
# echo 'irq:*' > /sys/kernel/debug/tracing/set_event
|
|
|
|
2.2 Via the 'enable' toggle
|
|
---------------------------
|
|
|
|
The events available are also listed in /sys/kernel/debug/tracing/events/ hierarchy
|
|
of directories.
|
|
|
|
To enable event 'sched_wakeup':
|
|
|
|
# echo 1 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable
|
|
|
|
To disable it:
|
|
|
|
# echo 0 > /sys/kernel/debug/tracing/events/sched/sched_wakeup/enable
|
|
|
|
To enable all events in sched subsystem:
|
|
|
|
# echo 1 > /sys/kernel/debug/tracing/events/sched/enable
|
|
|
|
To eanble all events:
|
|
|
|
# echo 1 > /sys/kernel/debug/tracing/events/enable
|
|
|
|
When reading one of these enable files, there are four results:
|
|
|
|
0 - all events this file affects are disabled
|
|
1 - all events this file affects are enabled
|
|
X - there is a mixture of events enabled and disabled
|
|
? - this file does not affect any event
|
|
|
|
2.3 Boot option
|
|
---------------
|
|
|
|
In order to facilitate early boot debugging, use boot option:
|
|
|
|
trace_event=[event-list]
|
|
|
|
The format of this boot option is the same as described in section 2.1.
|
|
|
|
3. Defining an event-enabled tracepoint
|
|
=======================================
|
|
|
|
See The example provided in samples/trace_events
|
|
|