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diff --git a/Documentation/libtracefs-synth2.txt b/Documentation/libtracefs-synth2.txt new file mode 100644 index 0000000..7e8e6cc --- /dev/null +++ b/Documentation/libtracefs-synth2.txt @@ -0,0 +1,281 @@ +libtracefs(3) +============= + +NAME +---- +tracefs_synth_create, tracefs_synth_destroy, tracefs_synth_complete, +tracefs_synth_trace, tracefs_synth_snapshot, tracefs_synth_save +- Creation of synthetic events + +SYNOPSIS +-------- +[verse] +-- +*#include <tracefs.h>* + +int *tracefs_synth_create*(struct tracefs_synth pass:[*]_synth_); +int *tracefs_synth_destroy*(struct tracefs_synth pass:[*]_synth_); +bool *tracefs_synth_complete*(struct tracefs_synth pass:[*]_synth_); + +int *tracefs_synth_trace*(struct tracefs_synth pass:[*]_synth_, + enum tracefs_synth_handler _type_, const char pass:[*]_var_); +int *tracefs_synth_snapshot*(struct tracefs_synth pass:[*]_synth_, + enum tracefs_synth_handler _type_, const char pass:[*]_var_); +int *tracefs_synth_save*(struct tracefs_synth pass:[*]_synth_, + enum tracefs_synth_handler _type_, const char pass:[*]_var_, + char pass:[**]_save_fields_); +-- + +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_create*() creates the synthetic event in the system. The synthetic events apply +across all instances. A synthetic event must be created with *tracefs_synth_alloc*(3) before +it can be created. + +*tracefs_synth_destroy*() destroys the synthetic event. It will attempt to stop the running of it in +its instance (top by default), but if its running in another instance this may fail as busy. + +*tracefs_synth_complete*() returns true if the synthetic event _synth_ has both +a starting and ending event. + +*tracefs_synth_trace*() Instead of doing just a trace on matching of the start and +end events, do the _type_ handler where *TRACEFS_SYNTH_HANDLE_MAX* will do a trace +when the given variable _var_ hits a new max for the matching keys. Or +*TRACEFS_SYNTH_HANDLE_CHANGE* for when the _var_ changes. _var_ must be one of +the _name_ elements used in *tracefs_synth_add_end_field*(3). + +*tracefs_synth_snapshot*() When the given variable _var_ is either a new max if +_handler_ is *TRACEFS_SYNTH_HANDLE_MAX* or simply changed if *TRACEFS_SYNTH_HANDLE_CHANGE* +then take a "snapshot" of the buffer. The snapshot moves the normal "trace" buffer +into a "snapshot" buffer, that can be accessed via the "snapshot" file in the +top level tracefs directory, or one of the instances. _var_ changes. _var_ must be one of +the _name_ elements used in *tracefs_synth_add_end_field*(3). + +*tracefs_synth_save*() When the given variable _var_ is either a new max if +_handler_ is *TRACEFS_SYNTH_HANDLE_MAX* or simpy changed if *TRACEFS_SYNTH_HANDLE_CHANGE* +then save the given _save_fields_ list. The fields will be stored in the histogram +"hist" file of the event that can be retrieved with *tracefs_event_file_read*(3). +_var_ must be one of the _name_ elements used in *tracefs_synth_add_end_field*(3). + +RETURN VALUE +------------ +All 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. + +[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 +-------- +*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_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). |