tracefs_synth_echo_cmd(3) — Linux manual page

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LIBTRACEFS(3)               libtracefs Manual              LIBTRACEFS(3)

NAME         top

       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         top

       #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         top

       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         top

       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         top

       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         top

       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         top

           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         top

       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         top

           Steven Rostedt <rostedt@goodmis.org[1]>
           Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>
           sameeruddin shaik <sameeruddin.shaik8@gmail.com[3]>

REPORTING BUGS         top

       Report bugs to <linux-trace-devel@vger.kernel.org[4]>

LICENSE         top

       libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES         top

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

COPYING         top

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

NOTES         top

        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

COLOPHON         top

       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 man-pages@man7.org

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)