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NAME |SYNOPSIS |DESCRIPTION |KEY TYPES |RETURN VALUE |EXAMPLE |FILES |SEE ALSO |AUTHOR |REPORTING BUGS |LICENSE |RESOURCES |COPYING |NOTES |COLOPHON | |
LIBTRACEFS(3) libtracefs ManualLIBTRACEFS(3)tracefs_hist_alloc, tracefs_hist_alloc_2d, tracefs_hist_alloc_nd, tracefs_hist_alloc_nd_cnt, tracefs_hist_free, tracefs_hist_add_key, tracefs_hist_add_key_cnt, tracefs_hist_add_value - Create and destroy event histograms
#include <tracefs.h> enumtracefs_hist_key_type{TRACEFS_HIST_KEY_NORMAL= 0,TRACEFS_HIST_KEY_HEX,TRACEFS_HIST_KEY_SYM,TRACEFS_HIST_KEY_SYM_OFFSET,TRACEFS_HIST_KEY_SYSCALL,TRACEFS_HIST_KEY_EXECNAME,TRACEFS_HIST_KEY_LOG,TRACEFS_HIST_KEY_USECS,TRACEFS_HIST_KEY_MAX }; structtracefs_hist_axis{ const char *key; enum tracefs_hist_key_typetype; }; struct tracefs_hist *tracefs_hist_alloc(struct tracefs_tep *tep, const char *system, const char *event, const char *key, enum tracefs_hist_key_typetype); struct tracefs_hist *tracefs_hist_alloc_2d(struct tracefs_tep *tep, const char *system, const char *event, const char *key1, enum tracefs_hist_key_typetype1, const char *key2, enum tracefs_hist_key_typetype2)); struct tracefs_hist *tracefs_hist_alloc_nd(struct tracefs_tep *tep, const char *system, const char *event, struct tracefs_hist_axis *axes); struct tracefs_hist *tracefs_hist_alloc_nd_cnt(struct tep_handle *tep, const char *system, const char *event_name, struct tracefs_hist_axis_cnt *axes); voidtracefs_hist_free(struct tracefs_hist *hist); inttracefs_hist_add_key(struct tracefs_hist *hist, const char *key, enum tracefs_hist_key_typetype); inttracefs_hist_add_key_cnt(struct tracefs_hist *hist, const char *key, enum tracefs_hist_key_typetype, intcnt); inttracefs_hist_add_value(struct tracefs_hist *hist, const char *value);Event histograms are created by the trigger file in the event directory. The syntax can be complex and difficult to get correct. This API handles the syntax, and facilitates the creation and interaction with the event histograms. Seehttps://www.kernel.org/doc/html/latest/trace/histogram.htmlfor more information.tracefs_hist_alloc() allocates a "struct tracefs_hist" descriptor of a one-dimensional histogram and returns the address of it. This descriptor must be freed bytracefs_hist_free(). Thetep is a trace event handle (seetracefs_local_events(3)), that holds thesystem andevent that the histogram will be attached to. Thesystem is the system or group of the event. Theevent is the event to attach the histogram to. Thekey is a field of the event that will be used as the key(dimension) of the histogram. Thetype is the type of thekey. See KEY TYPES below.tracefs_hist_alloc_2d() allocates a "struct tracefs_hist" descriptor of a two-dimensional histogram and returns the address of it. This descriptor must be freed bytracefs_hist_free(). Thetep is a trace event handle (seetracefs_local_events(3)), that holds thesystem andevent that the histogram will be attached to. Thesystem is the system or group of the event. Theevent is the event to attach the histogram to. Thekey1 is the first field of the event that will be used as the key(dimension) of the histogram. Thetype1 is the type of thekey1. See KEY TYPES below. Thekey2 is the second field of the event that will be used as the key(dimension) of the histogram. Thetype2 is the type of thekey2. See KEY TYPES below.tracefs_hist_alloc_nd() allocates a "struct tracefs_hist" descriptor of an N-dimensional histogram and returns the address of it. This descriptor must be freed bytracefs_hist_free(). Thetep is a trace event handle (seetracefs_local_events(3)), that holds thesystem andevent that the histogram will be attached to. Thesystem is the system or group of the event. Theevent is the event to attach the histogram to. Theaxes is an array ofkey /type pairs, defining the dimensions of the histogram.tracefs_hist_alloc_nd_cnt() will initialize a histogram descriptor that will be attached to thesystem/event. This only initializes the descriptor with the givenaxes keys as primaries. This only initializes the descriptor, it does not start the histogram in the kernel. The difference between this andtracefs_hist_alloc_nd()is that theaxes parameter is of typestruct tracefs_hist_axis_cnt and notstruct tracefs_hist_axis.tracefs_hist_free() frees thetracefs_hist descriptor. Note, it does not stop or disable the running histogram if it was started.tracefs_hist_destroy() needs to be called to do so.tracefs_hist_add_key() Adds a secondary or tertiary key to the histogram. The key passed totracefs_hist_alloc_nd() is the primary key of the histogram. The first time this function is called, it will add a secondary key (or two dimensional histogram). If this function is called again on the same histogram, it will add atertiary key (or three dimensional histogram). Thehist parameter is the histogram descriptor to add thekey to. Thetype is the type of key to add (See KEY TYPES below). Thetracefs_hist_add_key_cnt() is the same astracefs_hist_add_key() except that it allows to add a counter for the given type. Currently, there’s only thebucketstype that requires a counter. When adding a key with the buckets type,tracefs_hist_add_key() is not sufficient, as thebucketstype requires a counter or bucket size. Usetracefs_hist_add_key_cnt() when specifing a key that is broken up into buckets, and pass in the size of those buckets intocnt.tracefs_hist_add_value() will add a value to record. By default, the value is simply the "hitcount" of the number of times a instance of the histogram’s key was hit. Thehist is the histogram descriptor to add the value to. Thevalue is a field in the histogram to add to when an instance of the key is hit.
tracefs_hist_alloc_nd() andtracefs_hist_add_key() both add a key and requires that key to have a type. The types may be:TRACEFS_HIST_KEY_NORMALor zero (0) which is to not modify the type.TRACEFS_HIST_KEY_HEXto display the key in hex.TRACEFS_HIST_KEY_SYMto display the key as a kernel symbol (if found). If the key is an address, this is useful as it will display the function names instead of just a number.TRACEFS_HIST_KEY_SYM_OFFSETsimilar toTRACEFS_HIST_KEY_SYMbut will also include the offset of the function to match the exact address.TRACEFS_HIST_KEY_SYSCALLIf the key is a system call "id" (the number passed from user space to the kernel to tell it what system call it is calling), then the name of the system call is displayed.TRACEFS_HIST_KEY_EXECNAMEIf "common_pid" is the key (the pid of the executing task), instead of showing the number, show the name of the running task.TRACEFS_HIST_KEY_LOGwill display the key in a binary logarithmic scale.TRACEFS_HIST_KEY_USECSfor use with "common_timestamp" or TRACEFS_HIST_TIMESTAMP, in which case it will show the timestamp in microseconds instead of nanoseconds.
tracefs_hist_alloc_nd() returns an allocated histogram descriptor which must be freed bytracefs_hist_free() or NULL on error. All the other functions return zero on success or -1 on error. Iftracefs_hist_start() returns an error, a message may be displayed in the kernel that can be retrieved bytracefs_error_last().
#include <stdlib.h> #include <ctype.h> #include <unistd.h> #include <tracefs.h> enum commands { START, PAUSE, CONT, RESET, DELETE, SHOW, }; static void parse_system_event(char *group, char **system, char **event) { *system = strtok(group, "/"); *event = strtok(NULL, "/"); if (!*event) { *event = *system; *system = NULL; } } static int parse_keys(char *keys, struct tracefs_hist_axis_cnt **axes) { char *sav = NULL; char *key; int cnt = 0; for (key = strtok_r(keys, ",", &sav); key; key = strtok_r(NULL, ",", &sav)) { struct tracefs_hist_axis_cnt *ax; char *att; ax = realloc(*axes, sizeof(*ax) * (cnt + 2)); if (!ax) { perror("Failed to allocate axes"); exit(-1); } ax[cnt].key = key; ax[cnt].type = 0; ax[cnt + 1].key = NULL; ax[cnt + 1].type = 0; *axes = ax; att = strchr(key, '.'); if (att) { *att++ = '\0'; if (strcmp(att, "hex") == 0) ax[cnt].type = TRACEFS_HIST_KEY_HEX; else if (strcmp(att, "sym") == 0) ax[cnt].type = TRACEFS_HIST_KEY_SYM; else if (strcmp(att, "sym_offset") == 0) ax[cnt].type = TRACEFS_HIST_KEY_SYM_OFFSET; else if (strcmp(att, "syscall") == 0) ax[cnt].type = TRACEFS_HIST_KEY_SYSCALL; else if (strcmp(att, "exec") == 0) ax[cnt].type = TRACEFS_HIST_KEY_EXECNAME; else if (strcmp(att, "log") == 0) ax[cnt].type = TRACEFS_HIST_KEY_LOG; else if (strcmp(att, "usecs") == 0) ax[cnt].type = TRACEFS_HIST_KEY_USECS; else if (strncmp(att, "buckets", 7) == 0) { if (att[7] != '=' && !isdigit(att[8])) { fprintf(stderr, "'buckets' key type requires '=<size>'\n"); exit(-1); } ax[cnt].type = TRACEFS_HIST_KEY_BUCKETS; ax[cnt].cnt = atoi(&att[8]); } else { fprintf(stderr, "Undefined attribute '%s'\n", att); fprintf(stderr," Acceptable attributes:\n"); fprintf(stderr," hex, sym, sym_offset, syscall, exe, log, usecs\n"); exit(-1); } } cnt++; } return cnt; } static void process_hist(enum commands cmd, const char *instance_name, char *group, char *keys, char *vals, char *sort, char *ascend, char *desc) { struct tracefs_instance *instance = NULL; struct tracefs_hist *hist; struct tep_handle *tep; struct tracefs_hist_axis_cnt *axes = NULL; char *system; char *event; char *sav; char *val; int ret; int cnt; if (instance_name) { instance = tracefs_instance_create(instance_name); if (!instance) { fprintf(stderr, "Failed instance create\n"); exit(-1); } } tep = tracefs_local_events(NULL); if (!tep) { perror("Could not read events"); exit(-1); } parse_system_event(group, &system, &event); if (cmd == SHOW) { char *content; content = tracefs_event_file_read(instance, system, event, "hist", NULL); if (!content) { perror("Reading hist file"); exit(-1); } printf("%s\n", content); free(content); return; } if (!keys) { fprintf(stderr, "Command needs -k option\n"); exit(-1); } cnt = parse_keys(keys, &axes); if (!cnt) { fprintf(stderr, "No keys??\n"); exit(-1); } /* buckets require the nd_cnt function */ switch (cnt) { case 2: if (axes[1].type == TRACEFS_HIST_KEY_BUCKETS) cnt = -1; /* fall through */ case 1: if (axes[0].type == TRACEFS_HIST_KEY_BUCKETS) cnt = -1; } /* Show examples of hist1d and hist2d */ switch (cnt) { case 1: hist = tracefs_hist_alloc(tep, system, event, axes[0].key, axes[0].type); break; case 2: hist = tracefs_hist_alloc_2d(tep, system, event, axes[0].key, axes[0].type, axes[1].key, axes[1].type); break; default: /* Really, 1 and 2 could use this too */ hist = tracefs_hist_alloc_nd_cnt(tep, system, event, axes); } if (!hist) { fprintf(stderr, "Failed hist create\n"); exit(-1); } if (vals) { sav = NULL; for (val = strtok_r(vals, ",", &sav); val; val = strtok_r(NULL, ",", &sav)) { ret = tracefs_hist_add_value(hist, val); if (ret) { fprintf(stderr, "Failed to add value %s\n", val); exit(-1); } } } if (sort) { sav = NULL; for (val = strtok_r(sort, ",", &sav); val; val = strtok_r(NULL, ",", &sav)) { ret = tracefs_hist_add_sort_key(hist, val); if (ret) { fprintf(stderr, "Failed to add sort key/val %s\n", val); exit(-1); } } } if (ascend) { sav = NULL; for (val = strtok_r(ascend, ",", &sav); val; val = strtok_r(NULL, ",", &sav)) { ret = tracefs_hist_sort_key_direction(hist, val, TRACEFS_HIST_SORT_ASCENDING); if (ret) { fprintf(stderr, "Failed to add ascending key/val %s\n", val); exit(-1); } } } if (desc) { sav = NULL; for (val = strtok_r(desc, ",", &sav); val; val = strtok_r(NULL, ",", &sav)) { ret = tracefs_hist_sort_key_direction(hist, val, TRACEFS_HIST_SORT_DESCENDING); if (ret) { fprintf(stderr, "Failed to add descending key/val %s\n", val); exit(-1); } } } tracefs_error_clear(instance); switch (cmd) { case START: ret = tracefs_hist_start(instance, hist); if (ret) { char *err = tracefs_error_last(instance); if (err) fprintf(stderr, "\n%s\n", err); } break; case PAUSE: ret = tracefs_hist_pause(instance, hist); break; case CONT: ret = tracefs_hist_continue(instance, hist); break; case RESET: ret = tracefs_hist_reset(instance, hist); break; case DELETE: ret = tracefs_hist_destroy(instance, hist); break; case SHOW: /* Show was already done */ break; } if (ret) fprintf(stderr, "Failed: command\n"); exit(ret); } int main (int argc, char **argv, char **env) { enum commands cmd; char *instance = NULL; char *cmd_str; char *event = NULL; char *keys = NULL; char *vals = NULL; char *sort = NULL; char *desc = NULL; char *ascend = NULL; if (argc < 2) { fprintf(stderr, "usage: %s command [-B instance][-e [system/]event][-k keys][-v vals][-s sort]\n", argv[0]); fprintf(stderr, " [-a ascending][-d descending]\n"); exit(-1); } cmd_str = argv[1]; if (!strcmp(cmd_str, "start")) cmd = START; else if (!strcmp(cmd_str, "pause")) cmd = PAUSE; else if (!strcmp(cmd_str, "cont")) cmd = CONT; else if (!strcmp(cmd_str, "reset")) cmd = RESET; else if (!strcmp(cmd_str, "delete")) cmd = DELETE; else if (!strcmp(cmd_str, "show")) cmd = SHOW; else { fprintf(stderr, "Unknown command %s\n", cmd_str); exit(-1); } for (;;) { int c; c = getopt(argc - 1, argv + 1, "e:k:v:B:s:d:a:"); if (c == -1) break; switch (c) { case 'e': event = optarg; break; case 'k': keys = optarg; break; case 'v': vals = optarg; break; case 'B': instance = optarg; break; case 's': sort = optarg; break; case 'd': desc = optarg; break; case 'a': ascend = optarg; break; } } if (!event) { event = "kmem/kmalloc"; if (!keys) keys = "call_site.sym,bytes_req"; if (!vals) vals = "bytes_alloc"; if (!sort) sort = "bytes_req,bytes_alloc"; if (!desc) desc = "bytes_alloc"; } process_hist(cmd, instance, event, keys, vals, sort, ascend, desc); }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_pause(3),tracefs_hist_continue(3),tracefs_hist_reset(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_filter_pid_function(3), tracefs_filter_string_append(3), tracefs_hist_start(3), tracefs_sql(3), tracefs_synth_alloc(3), tracefs_synth_create(3), tracefs_synth_echo_cmd(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. | |