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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | COPYING | NOTES | COLOPHON |
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LIBTRACEFS(3) libtracefs Manual LIBTRACEFS(3)
tracefs_instance_get_stat, tracefs_instance_put_stat,
tracefs_buffer_stat_entries, tracefs_buffer_stat_overrun,
tracefs_buffer_stat_commit_overrun, tracefs_buffer_stat_bytes,
tracefs_buffer_stat_event_timestamp,
tracefs_buffer_stat_timestamp, tracefs_buffer_stat_dropped_events,
tracefs_buffer_stat_read_events - Handling tracing buffer stats
#include <tracefs.h>
struct tracefs_buffer_stat *tracefs_instance_get_stat(struct tracefs_instance *instance, int cpu);
void tracefs_instance_put_stat(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_entries(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_overrun(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_commit_overrun(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_bytes(struct tracefs_buffer_stat *tstat);
long long tracefs_buffer_stat_event_timestamp(struct tracefs_buffer_stat *tstat);
long long tracefs_buffer_stat_timestamp(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_dropped_events(struct tracefs_buffer_stat *tstat);
ssize_t tracefs_buffer_stat_read_events(struct tracefs_buffer_stat *tstat);
This set of functions read and parse the
tracefs/per_cpu/cpuX/stats file. These files hold the statistics
of the per CPU ring buffer, such as how many events are in the
ring buffer, how many have been read and so on.
The tracefs_instance_get_stat() function will read and parse a
given statistics file for a given instance and cpu. As the ring
buffer is split into per_cpu buffers, the information is only
associated to the given cpu. The returned tracefs_buffer_stat
pointer can be used with the other tracefs_buffer_stat functions
and must be freed with tracefs_instance_put_stat().
The tracefs_instance_put_stat() will free the resources allocated
for the given stat that was created by
tracefs_instance_get_stat().
The tracefs_buffer_stat_entries() returns the number of events
that are currently in the ring buffer associated with tstat.
The tracefs_buffer_stat_overrun() returns the number of events
that were lost by the ring buffer writer overrunning the reader.
The tracefs_buffer_stat_commit_overrun() returns the number of
events that were lost because the ring buffer was too small and an
interrupt interrupted a lower context event being recorded and it
added more events than the ring buffer could hold. Note this is
not a common occurrence and when it happens it means that
something was not set up properly.
The tracefs_buffer_stat_bytes() returns the number of bytes that
the current events take up. Note, it includes the meta data for
the events, but does not include the meta data for the
sub-buffers.
The tracefs_buffer_stat_event_timestamp() returns the timestamp of
the last event in the ring buffer.
The tracefs_buffer_stat_timestamp() returns the current timestamp
of the ring buffer. Note, it is only read when
tracefs_instance_get_stat() is called. It will have the timestamp
of the ring buffer when that function was called.
The tracefs_buffer_stat_dropped_events() returns the number of
events that were dropped if overwrite mode is disabled. It will
show the events that were lost because the writer caught up to the
reader and could not write any more events.
The tracefs_buffer_stat_read_events() returns the number of events
that were consumed by a reader.
The tracefs_instance_get_stat() returns a tracefs_buffer_stat
structure that can be used to retrieve the statistics via the
other functions. It must be freed with
tracefs_instance_put_stat().
The other functions that return different values from the
tracefs_buffer_stat structure all return the value, or -1 if the
value was not found.
#include <stdlib.h>
#include <unistd.h>
#include <tracefs.h>
int main(int argc, char **argv)
{
char *trace;
char buf[1000];
int ret;
int i;
for (i = 0; i < sizeof(buf) - 1; i++) {
buf[i] = '0' + i % 10;
}
buf[i] = '\0';
tracefs_instance_clear(NULL);
for (i = 0; i < 4; i++) {
ret = tracefs_printf(NULL, "%s\n", buf);
if (ret < 0)
perror("write");
}
trace = tracefs_instance_file_read(NULL, "trace", NULL);
printf("%s\n", trace);
free(trace);
for (i = 0; i < sysconf(_SC_NPROCESSORS_CONF); i++) {
struct tracefs_buffer_stat *tstat;
ssize_t entries, eread;
tstat = tracefs_instance_get_stat(NULL, i);
if (!tstat)
continue;
entries = tracefs_buffer_stat_entries(tstat);
eread = tracefs_buffer_stat_read_events(tstat);
if (!entries && !eread) {
tracefs_instance_put_stat(tstat);
continue;
}
printf("CPU: %d\n", i);;
printf("\tentries: %zd\n", entries);
printf("\toverrun: %zd\n", tracefs_buffer_stat_overrun(tstat));
printf("\tcommit_overrun: %zd\n", tracefs_buffer_stat_commit_overrun(tstat));
printf("\tbytes: %zd\n", tracefs_buffer_stat_bytes(tstat));
printf("\tevent_timestamp: %lld\n", tracefs_buffer_stat_event_timestamp(tstat));
printf("\ttimestamp: %lld\n", tracefs_buffer_stat_timestamp(tstat));
printf("\tdropped_events: %zd\n", tracefs_buffer_stat_dropped_events(tstat));
printf("\tread_events: %zd\n", eread);
tracefs_instance_put_stat(tstat);
}
}
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)
Steven Rostedt <rostedt@goodmis.org[1]>
Report bugs to <linux-trace-devel@vger.kernel.org[2]>
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. linux-trace-devel@vger.kernel.org
mailto:linux-trace-devel@vger.kernel.org
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
2025-02-02. (At that time, the date of the most recent commit
that was found in the repository was 2024-11-22.) 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 1.8.1 01/02/2025 LIBTRACEFS(3)
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HTML rendering created 2025-02-02 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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