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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |EXAMPLE |FILES |SEE ALSO |AUTHOR |REPORTING BUGS |LICENSE |RESOURCES |COPYING |NOTES |COLOPHON | |
LIBTRACEFS(3) libtracefs ManualLIBTRACEFS(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> inttracefs_instance_set_affinity(struct tracefs_instance *instance, const char *cpu_str); inttracefs_instance_set_affinity_set(struct tracefs_instance *instance, cpu_set_t *set, size_tset_size); inttracefs_instance_set_affinity_raw(struct tracefs_instance *instance, const char *mask); char *tracefs_instance_get_affinity(struct tracefs_instance *instance); inttracefs_instance_get_affinity_set(struct tracefs_instance *instance, cpu_set_t *set, size_tset_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 theinstance parameter. Ifinstance is NULL, then the top level instance is affected. Thetracefs_instance_set_affinity()function takes a stringcpu_str that is a list of CPUs to set the affinity for. Ifcpu_str is NULL, then all the CPUs in the system will be set. The format ofcpu_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. Thetracefs_instance_set_affinity_set()function takes a CPU set defined byCPU_SET(3). The size of the set defined byset_size is the size in bytes ofset. Ifset is NULL then all the CPUs on the system will be set, andset_size is ignored. Thetracefs_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. Thetracefs_instance_get_affinity()will retrieve the affinity in a human readable form. For example: "1,4,6-8" The string returned must be freed withfree(3). Thetracefs_instance_get_affinity_set()will set all the bits in the passed in cpu set (fromCPU_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. Thetracefs_instance_get_affinity_raw()will simply read the instance tracing_cpumask and return that string. The returned string must be freed withfree(3).
All the set functions return 0 on success and -1 on error. The functionstracefs_instance_get_affinity()andtracefs_instance_get_affinity_raw()returns an allocated string that must be freed withfree(3), or NULL on error. The functiontracefs_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:EFBIGif a CPU is set that is greater than what is in the system.EINVALOne of the parameters was invalid. The following errors are fortracefs_instance_set_affinity() andtracefs_instance_set_affinity_set():ENOMEMMemory allocation error.ENODEVdynamic events of requested type are not configured for the running kernel. The following errors are just fortracefs_instance_set_affinity()EACCESThecpu_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 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)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. | |