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