xref: /aosp_15_r20/external/libtracefs/Documentation/libtracefs-instances-affinity.txt (revision 287e80b3a36113050663245e7f2c00d274188f18)

libtracefs(3)
=============

NAME
----
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.

SYNOPSIS
--------
[verse]
--
*#include <tracefs.h>*

int *tracefs_instance_set_affinity*(struct tracefs_instance pass:[*]_instance_, const char pass:[*]_cpu_str_);
int *tracefs_instance_set_affinity_set*(struct tracefs_instance pass:[*]_instance_, cpu_set_t pass:[*]_set_, size_t _set_size_);
int *tracefs_instance_set_affinity_raw*(struct tracefs_instance pass:[*]_instance_, const char pass:[*]_mask_);

char pass:[*]*tracefs_instance_get_affinity*(struct tracefs_instance pass:[*]_instance_);
int *tracefs_instance_get_affinity_set*(struct tracefs_instance pass:[*]_instance_, cpu_set_t pass:[*]_set_, size_t _set_size_);
char pass:[*]*tracefs_instance_get_affinity_raw*(struct tracefs_instance pass:[*]_instance_);
--

DESCRIPTION
-----------
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).

RETURN VALUE
------------
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.


ERRORS
------
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.

EXAMPLE
-------
[source,c]
--
#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;
}
--
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)

AUTHOR
------
[verse]
--
*Steven Rostedt* <[email protected]>
*Tzvetomir Stoyanov* <[email protected]>
--
REPORTING BUGS
--------------
Report bugs to  <[email protected]>

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).