1SCHED_SETAFFINITY(2) Linux Programmer's Manual SCHED_SETAFFINITY(2)
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6 sched_setaffinity, sched_getaffinity - set and get a thread's CPU
7 affinity mask
8
10 #define _GNU_SOURCE /* See feature_test_macros(7) */
11 #include <sched.h>
12 int sched_setaffinity(pid_t pid, size_t cpusetsize,
14 const cpu_set_t *mask);
15 int sched_getaffinity(pid_t pid, size_t cpusetsize,
17 cpu_set_t *mask);
18
20 A thread's CPU affinity mask determines the set of CPUs on which it is
21 eligible to run. On a multiprocessor system, setting the CPU affinity
22 mask can be used to obtain performance benefits. For example, by dedi‐
23 cating one CPU to a particular thread (i.e., setting the affinity mask
24 of that thread to specify a single CPU, and setting the affinity mask
25 of all other threads to exclude that CPU), it is possible to ensure
26 maximum execution speed for that thread. Restricting a thread to run
27 on a single CPU also avoids the performance cost caused by the cache
28 invalidation that occurs when a thread ceases to execute on one CPU and
29 then recommences execution on a different CPU.
30 A CPU affinity mask is represented by the cpu_set_t structure, a "CPU
32 set", pointed to by mask. A set of macros for manipulating CPU sets is
33 described in CPU_SET(3).
34 sched_setaffinity() sets the CPU affinity mask of the thread whose ID
36 is pid to the value specified by mask. If pid is zero, then the call‐
37 ing thread is used. The argument cpusetsize is the length (in bytes)
38 of the data pointed to by mask. Normally this argument would be speci‐
39 fied as sizeof(cpu_set_t).
40 If the thread specified by pid is not currently running on one of the
42 CPUs specified in mask, then that thread is migrated to one of the CPUs
43 specified in mask.
44 sched_getaffinity() writes the affinity mask of the thread whose ID is
46 pid into the cpu_set_t structure pointed to by mask. The cpusetsize
47 argument specifies the size (in bytes) of mask. If pid is zero, then
48 the mask of the calling thread is returned.
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51 On success, sched_setaffinity() and sched_getaffinity() return 0. On
52 error, -1 is returned, and errno is set appropriately.
53
55 EFAULT A supplied memory address was invalid.
56 EINVAL The affinity bit mask mask contains no processors that are cur‐
58 rently physically on the system and permitted to the thread
59 according to any restrictions that may be imposed by cpuset
60 cgroups or the "cpuset" mechanism described in cpuset(7).
61 EINVAL (sched_getaffinity() and, in kernels before 2.6.9,
63 sched_setaffinity()) cpusetsize is smaller than the size of the
64 affinity mask used by the kernel.
65 EPERM (sched_setaffinity()) The calling thread does not have appropri‐
67 ate privileges. The caller needs an ef