Provided by: libtracefs-doc_1.6.4-1ubuntu1_all 
NAME
tracefs_synth_echo_cmd, tracefs_synth_get_start_hist, tracefs_synth_get_name,
tracefs_synth_raw_fmt, tracefs_synth_show_event, tracefs_synth_show_start_hist,
tracefs_synth_show_end_hist, tracefs_synth_get_event - Retrieve data of synthetic events.
SYNOPSIS
#include <tracefs.h>
int tracefs_synth_echo_cmd(struct trace_seq *seq, struct tracefs_synth *synth);
struct tracefs_hist *tracefs_synth_get_start_hist(struct tracefs_synth *synth);
const char *tracefs_synth_get_name(struct tracefs_synth *synth);
int tracefs_synth_raw_fmt(struct trace_seq *seq, struct tracefs_synth *synth);
const char *tracefs_synth_show_event(struct tracefs_synth *synth);
const char *tracefs_synth_show_start_hist(struct tracefs_synth *synth);
const char *tracefs_synth_show_end_hist(struct tracefs_synth *synth);
struct tep_event *tracefs_synth_get_event(struct tep_handle *tep, struct tracefs_synth *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.
See tracefs_synth_alloc(3) for allocation of synthetic events, and tracefs_synth_create()
for creating the synthetic event on the system.
tracefs_synth_echo_cmd() acts like tracefs_synth_create(), but instead of creating the
synthetic event in the system, it will write the echo commands to manually create it in
the seq given.
tracefs_synth_get_start_hist() returns a struct tracefs_hist descriptor describing the
histogram used to create the synthetic event.
enum tracefs_synth_handler {
TRACEFS_SYNTH_HANDLE_MATCH,
TRACEFS_SYNTH_HANDLE_MAX,
TRACEFS_SYNTH_HANDLE_CHANGE,
};
tracefs_synth_get_name() returns the name of the synthetic event or NULL on error. The
returned string belongs to the synth event object and is freed with the event by
tracefs_synth_free().
tracefs_synth_raw_fmt() writes the raw format strings (dynamic event and histograms) of
the synthetic event in the seq given.
tracefs_synth_show_event() returns the format of the dynamic event used by the synthetic
event or NULL on error. The returned string belongs to the synth event object and is freed
with the event by tracefs_synth_free().
tracefs_synth_show_start_hist() returns the format of the start histogram used by the
synthetic event or NULL on error. The returned string belongs to the synth event object
and is freed with the event by tracefs_synth_free().
tracefs_synth_show_end_hist() returns the format of the end histogram used by the
synthetic event or NULL on error. The returned string belongs to the synth event object
and is freed with the event by tracefs_synth_free().
The tracefs_synth_get_event() function returns a tep event, describing the given synthetic
event. The API detects any newly created or removed dynamic events. The returned pointer
to tep event is controlled by @tep and must not be freed.
RETURN VALUE
tracefs_synth_get_name(), tracefs_synth_show_event(), tracefs_synth_show_start_hist() and
tracefs_synth_show_end_hist() return a string owned by the synth event object.
The tracefs_synth_get_event() function returns a pointer to a tep event or NULL in case of
an error or if the requested synthetic event is missing. The returned pointer to tep event
is controlled by @tep and must not be freed.
All other functions return 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
See tracefs_sql(3) for a more indepth use of some of this code.
#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
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
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_alloc(3),
tracefs_synth_add_match_field(3), tracefs_synth_add_compare_field(3),
tracefs_synth_add_start_field(3), tracefs_synth_add_end_field(3),
tracefs_synth_append_start_filter(3), tracefs_synth_append_end_filter(3),
tracefs_synth_free(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),
AUTHOR
Steven Rostedt <rostedt@goodmis.org[1]>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>
sameeruddin shaik <sameeruddin.shaik8@gmail.com[3]>
REPORTING BUGS
Report bugs to <linux-trace-devel@vger.kernel.org[4]>
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).
NOTES
1. rostedt@goodmis.org
mailto:rostedt@goodmis.org
2. tz.stoyanov@gmail.com
mailto:tz.stoyanov@gmail.com
3. sameeruddin.shaik8@gmail.com
mailto:sameeruddin.shaik8@gmail.com
4. linux-trace-devel@vger.kernel.org
mailto:linux-trace-devel@vger.kernel.org