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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | COPYING | NOTES | COLOPHON |
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LIBTRACEFS(3) libtracefs Manual LIBTRACEFS(3)
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.
#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);
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.
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.
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.
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;
}
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.
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),
Steven Rostedt <[email protected][1]>
Tzvetomir Stoyanov <[email protected][2]>
sameeruddin shaik <[email protected][3]>
Report bugs to <[email protected][4]>
libtracefs is Free Software licensed under the GNU LGPL 2.1
https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/
Copyright (C) 2020 VMware, Inc. Free use of this software is
granted under the terms of the GNU Public License (GPL).
1. [email protected]
mailto:[email protected]
2. [email protected]
mailto:[email protected]
3. [email protected]
mailto:[email protected]
4. [email protected]
mailto:[email protected]
This page is part of the libtracefs (Linux kernel trace file
system library) project. Information about the project can be
found at ⟨https://www.trace-cmd.org/⟩. If you have a bug report
for this manual page, see ⟨https://www.trace-cmd.org/⟩. This
page was obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git⟩ on
2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-05-17.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to [email protected]
libtracefs 1.7.0 12/22/2023 LIBTRACEFS(3)
Pages that refer to this page: tracefs_sql(3), tracefs_synth_alloc(3), tracefs_synth_create(3)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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