path: root/Documentation/libtracefs-synth.txt

libtracefs(3)
=============

NAME
----
tracefs_synth_alloc, tracefs_synth_add_match_field, tracefs_synth_add_compare_field, tracefs_synth_add_start_field,
tracefs_synth_add_end_field, tracefs_synth_append_start_filter, tracefs_synth_append_end_filter, tracefs_synth_free,
- Creation of a synthetic event descriptor

SYNOPSIS
--------
[verse]
--
*#include <tracefs.h>*

struct tracefs_synth pass:[*]*tracefs_synth_alloc*(struct tep_handle pass:[*]_tep_,
					 const char pass:[*]_name_,
					 const char pass:[*]_start_system_,
					 const char pass:[*]_start_event_,
					 const char pass:[*]_end_system_,
					 const char pass:[*]_end_event_,
					 const char pass:[*]_start_match_field_,
					 const char pass:[*]_end_match_field_,
					 const char pass:[*]_match_name_);
int *tracefs_synth_add_match_field*(struct tracefs_synth pass:[*]_synth_,
				  const char pass:[*]_start_match_field_,
				  const char pass:[*]_end_match_field_,
				  const char pass:[*]_name_);
int *tracefs_synth_add_compare_field*(struct tracefs_synth pass:[*]_synth_,
				    const char pass:[*]_start_compare_field_,
				    const char pass:[*]_end_compare_field_,
				    enum tracefs_synth_calc _calc_,
				    const char pass:[*]_name_);
int *tracefs_synth_add_start_field*(struct tracefs_synth pass:[*]_synth_,
				  const char pass:[*]_start_field_,
				  const char pass:[*]_name_);
int *tracefs_synth_add_end_field*(struct tracefs_synth pass:[*]_synth_,
				const char pass:[*]_end_field_,
				const char pass:[*]_name_);
int *tracefs_synth_append_start_filter*(struct tracefs_synth pass:[*]_synth_,
				      struct tracefs_filter _type_,
				      const char pass:[*]_field_,
				      enum tracefs_synth_compare _compare_,
				      const char pass:[*]_val_);
int *tracefs_synth_append_end_filter*(struct tracefs_synth pass:[*]_synth_,
				    struct tracefs_filter _type_,
				    const char pass:[*]_field_,
				    enum tracefs_synth_compare _compare_,
				    const char pass:[*]_val_);
void *tracefs_synth_free*(struct tracefs_synth pass:[*]_synth_);
--

DESCRIPTION
-----------
Synthetic events are dynamic events that are created by matching
two other events which triggers a synthetic event. One event is the starting
event which some field is recorded, and when the second event is executed,
if it has a field (or fields) that matches the starting event's field (or fields)
then it will trigger the synthetic event. The field values other than the matching
fields may be passed from the starting event to the end event to perform calculations
on, or to simply pass as a parameter to the synthetic event.

One common use case is to set "sched_waking" as the starting event. This event is
triggered when a process is awoken. Then set "sched_switch" as the ending event.
This event is triggered when a new task is scheduled on the CPU. By setting
the "common_pid" of both events as the matching fields, the time between the
two events is considered the wake up latency of that process. Use *TRACEFS_TIMESTAMP*
as a field for both events to calculate the delta in nanoseconds, or use
*TRACEFS_TIMESTAMP_USECS" as the compare fields for both events to calculate the
delta in microseconds. This is used as the example below.

*tracefs_synth_alloc*() allocates and initializes a synthetic event.
It does not create the synthetic event, but supplies the minimal information
to do so. See *tracefs_synth_create*(3) for how to create the synthetic
event in the system. It requires a _tep_ handler that can be created by
*tracefs_local_events*(3) for more information. The _name_ holds the name
of the synthetic event that will be created. The _start_system_ is the name
of the system for the starting event. It may be NULL and the first event
with the name of _start_event_ will be chosen. The _end_system_ is the
name of the system for theh ending event. It may be NULL and the first event
with the name of _end_event_ will be chosen as the ending event. If _match_name_
is given, then this will be the field of the created synthetic event that
holds the matching keys of the starting event's _start_match_field_ and
the ending event's _end_match_field_. If _match_name_ is NULL, then it will
not be recorded in the created synthetic event.

*tracefs_synth_add_match_field*() will add a second key to match between the
starting event and the ending event. If _name_ is given, then the content
of the matching field will be saved by this _name_ in the synthetic event.
The _start_match_field_ is the field of the starting event to mach with the
ending event's _end_match_field_.

*tracefs_synth_add_compare_field*() is used to compare the _start_compare_field_
of the starting event with the _end_compare_field_ of the ending event. The _name_
must be given so that the result will be saved by the synthetic event. It makes
no sense to not pass this to the synthetic event after doing the work of
the compared fields, as it serves no other purpose. The _calc_ parameter
can be one of:

*TRACEFS_SYNTH_DELTA_END* - calculate the difference between the content in
 the _end_compare_field_ from the content of the _start_compare_field_.

_name_ = _end_compare_field_ - _start_compare_field_

*TRACEFS_SYNTH_DELTA_START* - calculate the difference between the content in
 the _start_compare_field_ from the content of the _end_compare_field_.

_name_ = _start_compare_field_ - _end_compare_field_

*TRACEFS_SYNTH_ADD* - Add the content of the _start_compare_field_ to the
  content of the _end_compare_field_.

_name_ = _start_compare_field_ + _end_compare_field_

*tracefs_synth_add_start_field*() - Records the _start_field_ of the starting
event as _name_ in the synthetic event. If _name_ is NULL, then the name used
will be the same as _start_field_.

*tracefs_synth_add_end_field*() - Records the _end_field_ of the ending
event as _name_ in the synthetic event. If _name_ is NULL, then the name used
will be the same as _end_field_.

*tracefs_synth_append_start_filter*() creates a filter or appends to it for the
starting event. Depending on _type_, it will build a string of tokens for
parenthesis or logic statements, or it may add a comparison of _field_
to _val_ based on _compare_.

If _type_ is:
*TRACEFS_FILTER_COMPARE*     -  See below
*TRACEFS_FILTER_AND*         -  Append "&&" to the filter
*TRACEFS_FILTER_OR*          -  Append "||" to the filter
*TRACEFS_FILTER_NOT*         -  Append "!" to the filter
*TRACEFS_FILTER_OPEN_PAREN*  -  Append "(" to the filter
*TRACEFS_FILTER_CLOSE_PAREN* -  Append ")" to the filter

_field_, _compare_, and _val_ are ignored unless _type_ is equal to
*TRACEFS_FILTER_COMPARE*, then _compare will be used for the following:

*TRACEFS_COMPARE_EQ* - _field_ == _val_

*TRACEFS_COMPARE_NE* - _field_ != _val_

*TRACEFS_COMPARE_GT* - _field_ > _val_

*TRACEFS_COMPARE_GE* - _field_ >= _val_

*TRACEFS_COMPARE_LT* - _field_ < _val_

*TRACEFS_COMPARE_LE* - _field_ <pass:[=] _val_

*TRACEFS_COMPARE_RE* - _field_ ~ "_val_" : where _field_ is a string.

*TRACEFS_COMPARE_AND* - _field_ & _val_ : where _field_ is a flags field.

*tracefs_synth_append_end_filter*() is the same as *tracefs_synth_append_start_filter* but
filters on the ending event.

*tracefs_synth_free*() frees the allocated descriptor returned by
*tracefs_synth_alloc*().

RETURN VALUE
------------
*tracefs_synth_alloc*() returns an allocated struct tracefs_synth descriptor
on success or NULL on error.

All other functions that return an integer returns zero on success or -1
on error.

ERRORS
------
The following errors are for all the above calls:

*EPERM* Not run as root user when required.

*EINVAL* Either a parameter is not valid (NULL when it should not be)
  or a field that is not compatible for calculations.

*ENODEV* An event or one of its fields is not found.

*EBADE* The fields of the start and end events are not compatible for
  either matching or comparing.

*ENOMEM* not enough memory is available.

And more errors may have happened from the system calls to the system.

EXAMPLE
-------
[source,c]
--
#include <stdlib.h>
#include <tracefs.h>

#define start_event "sched_waking"
#define start_field "pid"

#define end_event "sched_switch"
#define end_field "next_pid"

#define match_name "pid"

static struct tracefs_synth *synth;

static void make_event(void)
{
	struct tep_handle *tep;

	/* Load all events from the system */
	tep = tracefs_local_events(NULL);

	/* Initialize the synthetic event */
	synth = tracefs_synth_alloc(tep, "wakeup_lat",
				    NULL, start_event,
				    NULL, end_event,
				    start_field, end_field,
				    match_name);

	/* The tep is no longer needed */
	tep_free(tep);


	/* Save the "prio" field as "prio" from the start event */
	tracefs_synth_add_start_field(synth, "prio", NULL);

	/* Save the "next_comm" as "comm" from the end event */
	tracefs_synth_add_end_field(synth, "next_comm", "comm");

	/* Save the "prev_prio" as "prev_prio" from the end event */
	tracefs_synth_add_end_field(synth, "prev_prio", NULL);

	/*
	 * Take a microsecond time difference between end and start
	 * and record as "delta"
	 */
	tracefs_synth_add_compare_field(synth, TRACEFS_TIMESTAMP_USECS,
					TRACEFS_TIMESTAMP_USECS,
					TRACEFS_SYNTH_DELTA_END, "delta");

	/* Only record if start event "prio" is less than 100 */
	tracefs_synth_append_start_filter(synth, TRACEFS_FILTER_COMPARE,
					  "prio", TRACEFS_COMPARE_LT, "100");

	/*
	 * Only record if end event "next_prio" is less than 50
	 * or the previous task's prio was not greater than or equal to 100.
	 *   next_prio < 50 || !(prev_prio >= 100)
	 */
	tracefs_synth_append_end_filter(synth, TRACEFS_FILTER_COMPARE,
					"next_prio", TRACEFS_COMPARE_LT, "50");
	tracefs_synth_append_end_filter(synth, TRACEFS_FILTER_OR, NULL, 0, NULL);
	tracefs_synth_append_end_filter(synth, TRACEFS_FILTER_NOT, NULL, 0, NULL);
	tracefs_synth_append_end_filter(synth, TRACEFS_FILTER_OPEN_PAREN, NULL, 0, NULL);
	tracefs_synth_append_end_filter(synth, TRACEFS_FILTER_COMPARE,
					"prev_prio", TRACEFS_COMPARE_GE, "100");
	/*
	 * Note, the above only added: "next_prio < 50 || !(prev_prio >= 100"
	 * That's because, when the synth is executed, the remaining close parenthesis
	 * will be added. That is, the string will end up being:
	 * "next_prio < 50 || !(prev_prio >= 100)" when one of tracefs_sync_create()
	 * or tracefs_sync_echo_cmd() is run.
	 */
}

/* Display how to create the synthetic event */
static void show_event(void)
{
	struct trace_seq s;

	trace_seq_init(&s);

	tracefs_synth_echo_cmd(&s, synth);
	trace_seq_terminate(&s);
	trace_seq_do_printf(&s);
	trace_seq_destroy(&s);
}

int main (int argc, char **argv)
{
	make_event();

	if (argc > 1) {
		if (!strcmp(argv[1], "create")) {
			/* Create the synthetic event */
			tracefs_synth_create(synth);
		} else if (!strcmp(argv[1], "delete")) {
			/* Delete the synthetic event */
			tracefs_synth_destroy(synth);
		} else {
			printf("usage: %s [create|delete]\n", argv[0]);
			exit(-1);
		}
	} else
		show_event();

	tracefs_synth_free(synth);

	return 0;
}
--

FILES
-----
[verse]
--
*tracefs.h*
	Header file to include in order to have access to the library APIs.
*-ltracefs*
	Linker switch to add when building a program that uses the library.
--

SEE ALSO
--------
*tracefs_synth_create*(3),
*tracefs_synth_destroy*(3),
*tracfes_synth_echo_cmd*(3),
*libtracefs*(3),
*libtraceevent*(3),
*trace-cmd*(1),
*tracefs_hist_alloc*(3),
*tracefs_hist_alloc_2d*(3),
*tracefs_hist_alloc_nd*(3),
*tracefs_hist_free*(3),
*tracefs_hist_add_key*(3),
*tracefs_hist_add_value*(3),
*tracefs_hist_add_name*(3),
*tracefs_hist_start*(3),
*tracefs_hist_destory*(3),
*tracefs_hist_add_sort_key*(3),
*tracefs_hist_sort_key_direction*(3),
*tracefs_synth_create*(3),
*tracefs_synth_destroy*(3),
*tracefs_synth_complete*(3),
*tracefs_synth_trace*(3),
*tracefs_synth_snapshot*(3),
*tracefs_synth_save*(3),
*tracefs_synth_echo_cmd*(3),
*tracefs_synth_get_start_hist*(3),
*tracefs_synth_get_name*(3),
*tracefs_synth_raw_fmt*(3),
*tracefs_synth_show_event*(3),
*tracefs_synth_show_start_hist*(3),
*tracefs_synth_show_end_hist*(3),
*tracefs_synth_get_event*(3),

AUTHOR
------
[verse]
--
*Steven Rostedt* <rostedt@goodmis.org>
*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
*sameeruddin shaik* <sameeruddin.shaik8@gmail.com>
--
REPORTING BUGS
--------------
Report bugs to  <linux-trace-devel@vger.kernel.org>

LICENSE
-------
libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES
---------
https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/

COPYING
-------
Copyright \(C) 2020 VMware, Inc. Free use of this software is granted under
the terms of the GNU Public License (GPL).