|
HTML rendering created 2025-09-06 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. |
|
|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLE | FILES | SEE ALSO | AUTHOR | REPORTING BUGS | LICENSE | RESOURCES | COPYING | NOTES | COLOPHON |
|
|
|
LIBTRACEFS(3) libtracefs Manual LIBTRACEFS(3)
tracefs_instance_set_affinity, tracefs_instance_set_affinity_set,
tracefs_instance_set_affinity_raw, tracefs_instance_get_affinity,
tracefs_instance_get_affinity_set,
tracefs_instance_get_affinity_raw - Sets or retrieves the affinity
for an instance or top level for what CPUs enable tracing.
#include <tracefs.h>
int tracefs_instance_set_affinity(struct tracefs_instance *instance, const char *cpu_str);
int tracefs_instance_set_affinity_set(struct tracefs_instance *instance, cpu_set_t *set, size_t set_size);
int tracefs_instance_set_affinity_raw(struct tracefs_instance *instance, const char *mask);
char *tracefs_instance_get_affinity(struct tracefs_instance *instance);
int tracefs_instance_get_affinity_set(struct tracefs_instance *instance, cpu_set_t *set, size_t set_size);
char *tracefs_instance_get_affinity_raw(struct tracefs_instance *instance);
These functions set or retrieve the CPU affinity that limits what
CPUs will have tracing enabled for a given instance defined by the
instance parameter. If instance is NULL, then the top level
instance is affected.
The tracefs_instance_set_affinity() function takes a string
cpu_str that is a list of CPUs to set the affinity for. If cpu_str
is NULL, then all the CPUs in the system will be set. The format
of cpu_str is a comma delimited string of decimal numbers with no
spaces. A range may be specified by a hyphen.
For example: "1,4,6-8"
The numbers do not need to be in order except for ranges, where
the second number must be equal to or greater than the first.
The tracefs_instance_set_affinity_set() function takes a CPU set
defined by CPU_SET(3). The size of the set defined by set_size is
the size in bytes of set. If set is NULL then all the CPUs on the
system will be set, and set_size is ignored.
The tracefs_instance_set_affinity_raw() function takes a string
that holds a hexidecimal bitmask, where each 32 bits is separated
by a comma. For a machine with more that 32 CPUs, to set CPUS 1-10
and CPU 40:
"100,000007fe"
Where the above is a hex representation of bits 1-10 and bit 40
being set.
The tracefs_instance_get_affinity() will retrieve the affinity in
a human readable form.
For example: "1,4,6-8"
The string returned must be freed with free(3).
The tracefs_instance_get_affinity_set() will set all the bits in
the passed in cpu set (from CPU_SET(3)). Note it will not clear
any bits that are already set in the set but the CPUs are not. If
only the bits for the CPUs that are enabled should be set, a
CPU_ZERO_S() should be performed on the set before calling this
function.
The tracefs_instance_get_affinity_raw() will simply read the
instance tracing_cpumask and return that string. The returned
string must be freed with free(3).
All the set functions return 0 on success and -1 on error.
The functions tracefs_instance_get_affinity() and
tracefs_instance_get_affinity_raw() returns an allocated string
that must be freed with free(3), or NULL on error.
The function tracefs_instance_get_affinity_set() returns the
number of CPUs that were found set, or -1 on error.
The following errors are for all the above calls:
EFBIG if a CPU is set that is greater than what is in the system.
EINVAL One of the parameters was invalid.
The following errors are for tracefs_instance_set_affinity() and
tracefs_instance_set_affinity_set():
ENOMEM Memory allocation error.
ENODEV dynamic events of requested type are not configured for the
running kernel.
The following errors are just for tracefs_instance_set_affinity()
EACCES The cpu_str was modified by another thread when processing
it.
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>
#include <tracefs.h>
int main (int argc, char **argv)
{
struct trace_seq seq;
cpu_set_t *set;
size_t set_size;
char *c;
int cpu1;
int cpu2;
int i;
c = tracefs_instance_get_affinity(NULL);
printf("The affinity was %s\n", c);
free(c);
if (argc < 2) {
tracefs_instance_set_affinity(NULL, NULL);
exit(0);
}
/* Show example using a set */
if (argc == 2 && !strchr(argv[1],',')) {
cpu1 = atoi(argv[1]);
c = strchr(argv[1], '-');
if (c++)
cpu2 = atoi(c);
else
cpu2 = cpu1;
if (cpu2 < cpu1) {
fprintf(stderr, "Invalid CPU range\n");
exit(-1);
}
set = CPU_ALLOC(cpu2 + 1);
set_size = CPU_ALLOC_SIZE(cpu2 + 1);
CPU_ZERO_S(set_size, set);
for ( ; cpu1 <= cpu2; cpu1++)
CPU_SET(cpu1, set);
tracefs_instance_set_affinity_set(NULL, set, set_size);
CPU_FREE(set);
exit(0);
}
trace_seq_init(&seq);
for (i = 1; i < argc; i++) {
if (i > 1)
trace_seq_putc(&seq, ',');
trace_seq_puts(&seq, argv[i]);
}
trace_seq_terminate(&seq);
tracefs_instance_set_affinity(NULL, seq.buffer);
trace_seq_destroy(&seq);
exit(0);
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)
Steven Rostedt <rostedt@goodmis.org[1]>
Tzvetomir Stoyanov <tz.stoyanov@gmail.com[2]>
Report bugs to <linux-trace-devel@vger.kernel.org[3]>
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. 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
2025-08-11. (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 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)
|
HTML rendering created 2025-09-06 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. |
|