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diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt deleted file mode 100644 index bb24c2a0e87..00000000000 --- a/Documentation/trace/events.txt +++ /dev/null @@ -1,280 +0,0 @@ - Event Tracing - - Documentation written by Theodore Ts'o - Updated by Li Zefan and Tom Zanussi - -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 enable 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] - -event-list is a comma separated list of events. See section 2.1 for event -format. - -3. Defining an event-enabled tracepoint -======================================= - -See The example provided in samples/trace_events - -4. Event formats -================ - -Each trace event has a 'format' file associated with it that contains -a description of each field in a logged event. This information can -be used to parse the binary trace stream, and is also the place to -find the field names that can be used in event filters (see section 5). - -It also displays the format string that will be used to print the -event in text mode, along with the event name and ID used for -profiling. - -Every event has a set of 'common' fields associated with it; these are -the fields prefixed with 'common_'. The other fields vary between -events and correspond to the fields defined in the TRACE_EVENT -definition for that event. - -Each field in the format has the form: - - field:field-type field-name; offset:N; size:N; - -where offset is the offset of the field in the trace record and size -is the size of the data item, in bytes. - -For example, here's the information displayed for the 'sched_wakeup' -event: - -# cat /sys/kernel/debug/tracing/events/sched/sched_wakeup/format - -name: sched_wakeup -ID: 60 -format: - field:unsigned short common_type; offset:0; size:2; - field:unsigned char common_flags; offset:2; size:1; - field:unsigned char common_preempt_count; offset:3; size:1; - field:int common_pid; offset:4; size:4; - field:int common_tgid; offset:8; size:4; - - field:char comm[TASK_COMM_LEN]; offset:12; size:16; - field:pid_t pid; offset:28; size:4; - field:int prio; offset:32; size:4; - field:int success; offset:36; size:4; - field:int cpu; offset:40; size:4; - -print fmt: "task %s:%d [%d] success=%d [%03d]", REC->comm, REC->pid, - REC->prio, REC->success, REC->cpu - -This event contains 10 fields, the first 5 common and the remaining 5 -event-specific. All the fields for this event are numeric, except for -'comm' which is a string, a distinction important for event filtering. - -5. Event filtering -================== - -Trace events can be filtered in the kernel by associating boolean -'filter expressions' with them. As soon as an event is logged into -the trace buffer, its fields are checked against the filter expression -associated with that event type. An event with field values that -'match' the filter will appear in the trace output, and an event whose -values don't match will be discarded. An event with no filter -associated with it matches everything, and is the default when no -filter has been set for an event. - -5.1 Expression syntax ---------------------- - -A filter expression consists of one or more 'predicates' that can be -combined using the logical operators '&&' and '||'. A predicate is -simply a clause that compares the value of a field contained within a -logged event with a constant value and returns either 0 or 1 depending -on whether the field value matched (1) or didn't match (0): - - field-name relational-operator value - -Parentheses can be used to provide arbitrary logical groupings and -double-quotes can be used to prevent the shell from interpreting -operators as shell metacharacters. - -The field-names available for use in filters can be found in the -'format' files for trace events (see section 4). - -The relational-operators depend on the type of the field being tested: - -The operators available for numeric fields are: - -==, !=, <, <=, >, >= - -And for string fields they are: - -==, != - -Currently, only exact string matches are supported. - -5.2 Setting filters -------------------- - -A filter for an individual event is set by writing a filter expression -to the 'filter' file for the given event. - -For example: - -# cd /sys/kernel/debug/tracing/events/sched/sched_wakeup -# echo "common_preempt_count > 4" > filter - -A slightly more involved example: - -# cd /sys/kernel/debug/tracing/events/signal/signal_generate -# echo "((sig >= 10 && sig < 15) || sig == 17) && comm != bash" > filter - -If there is an error in the expression, you'll get an 'Invalid -argument' error when setting it, and the erroneous string along with -an error message can be seen by looking at the filter e.g.: - -# cd /sys/kernel/debug/tracing/events/signal/signal_generate -# echo "((sig >= 10 && sig < 15) || dsig == 17) && comm != bash" > filter --bash: echo: write error: Invalid argument -# cat filter -((sig >= 10 && sig < 15) || dsig == 17) && comm != bash -^ -parse_error: Field not found - -Currently the caret ('^') for an error always appears at the beginning of -the filter string; the error message should still be useful though -even without more accurate position info. - -5.3 Clearing filters --------------------- - -To clear the filter for an event, write a '0' to the event's filter -file. - -To clear the filters for all events in a subsystem, write a '0' to the -subsystem's filter file. - -5.3 Subsystem filters ---------------------- - -For convenience, filters for every event in a subsystem can be set or -cleared as a group by writing a filter expression into the filter file -at the root of the subsystem. Note however, that if a filter for any -event within the subsystem lacks a field specified in the subsystem -filter, or if the filter can't be applied for any other reason, the -filter for that event will retain its previous setting. This can -result in an unintended mixture of filters which could lead to -confusing (to the user who might think different filters are in -effect) trace output. Only filters that reference just the common -fields can be guaranteed to propagate successfully to all events. - -Here are a few subsystem filter examples that also illustrate the -above points: - -Clear the filters on all events in the sched subsystem: - -# cd /sys/kernel/debug/tracing/events/sched -# echo 0 > filter -# cat sched_switch/filter -none -# cat sched_wakeup/filter -none - -Set a filter using only common fields for all events in the sched -subsystem (all events end up with the same filter): - -# cd /sys/kernel/debug/tracing/events/sched -# echo common_pid == 0 > filter -# cat sched_switch/filter -common_pid == 0 -# cat sched_wakeup/filter -common_pid == 0 - -Attempt to set a filter using a non-common field for all events in the -sched subsystem (all events but those that have a prev_pid field retain -their old filters): - -# cd /sys/kernel/debug/tracing/events/sched -# echo prev_pid == 0 > filter -# cat sched_switch/filter -prev_pid == 0 -# cat sched_wakeup/filter -common_pid == 0 |