Newer
Older
Event Tracing
Documentation written by Theodore Ts'o
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
2. Using Event Tracing
======================
2.1 Via the 'set_event' interface
---------------------------------
The events which are available for tracing can be found in the file
To enable a particular event, such as 'sched_wakeup', simply echo it
to /debug/tracing/set_event. For example:
# echo sched_wakeup >> /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' >> /debug/tracing/set_event
To disable all events, echo an empty line to the set_event file:
# echo > /debug/tracing/set_event
To enable all events, echo '*:*' or '*:' to the set_event file:
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:
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
# echo 'irq:*' > /debug/tracing/set_event
2.2 Via the 'enable' toggle
---------------------------
The events available are also listed in /debug/tracing/events/ hierarchy
of directories.
To enable event 'sched_wakeup':
# echo 1 > /debug/tracing/events/sched/sched_wakeup/enable
To disable it:
# echo 0 > /debug/tracing/events/sched/sched_wakeup/enable
To enable all events in sched subsystem:
# echo 1 > /debug/tracing/events/sched/enable
To eanble all events:
# echo 1 > /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
3. Defining an event-enabled tracepoint
=======================================
See The example provided in samples/trace_events