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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |EXAMPLE |FILES |SEE ALSO |AUTHOR |REPORTING BUGS |LICENSE |RESOURCES |COPYING |NOTES |COLOPHON | |
LIBTRACEFS(3) libtracefs ManualLIBTRACEFS(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> inttracefs_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); inttracefs_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. UseTRACEFS_TIMESTAMPas a field for both events to calculate the delta in nanoseconds, or useTRACEFS_TIMESTAMP_USECSas the compare fields for both events to calculate the delta in microseconds. This is used as the example below. Seetracefs_synth_alloc(3) for allocation of synthetic events, andtracefs_synth_create() for creating the synthetic event on the system.tracefs_synth_echo_cmd() acts liketracefs_synth_create(), but instead of creating the synthetic event in the system, it will write the echo commands to manually create it in theseq 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 bytracefs_synth_free().tracefs_synth_raw_fmt() writes the raw format strings (dynamic event and histograms) of the synthetic event in theseq 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 bytracefs_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 bytracefs_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 bytracefs_synth_free(). Thetracefs_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() andtracefs_synth_show_end_hist() return a string owned by the synth event object. Thetracefs_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:EPERMNot run as root user when required.EINVALEither a parameter is not valid (NULL when it should not be) or a field that is not compatible for calculations.ENODEVAn event or one of its fields is not found.EBADEThe fields of the start and end events are not compatible for either matching or comparing.ENOMEMnot enough memory is available. And more errors may have happened from the system calls to the system.
Seetracefs_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<rostedt@goodmis.org[1]>Tzvetomir Stoyanov<tz.stoyanov@gmail.com[2]>sameeruddin shaik<sameeruddin.shaik8@gmail.com[3]>
Report bugs to <linux-trace-devel@vger.kernel.org[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. 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
This page is part of thelibtracefs (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 2025-08-11. (At that time, the date of the most recent commit that was found in the repository was 2025-06-02.) 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 isnot part of the original manual page), send a mail to man-pages@man7.orglibtracefs 1.7.0 12/22/2023LIBTRACEFS(3)Pages that refer to this page:tracefs_sql(3), tracefs_synth_alloc(3), tracefs_synth_create(3)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |