libc/sys/sched_setaffinity.2

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.Dd January 14, 2017
.Dt SCHED_SETAFFINITY 2
.Os
.Sh NAME
.Nm sched_setaffinity,
.Nm sched_getaffinity
.Nd set and get a process's CPU affinity mask
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/types.h
.In sys/sched.h
.Ft int
.Fn sched_setaffinity "pid_t pid" "size_t cpusetsize" "const cpu_set_t *mask"
.Ft int
.Fn sched_getaffinity "pid_t pid" "size_t cpusetsize" "cpu_set_t *mask"
.Fn CPU_ZERO &mask
.Fn CPU_SET cpu &mask
.Fn CPU_CLR cpu &mask
.Fn CPU_ISSET cpu &mask
.Fn CPU_COUNT &mask
.Fn CPU_AND &dstmask &srcmask1 &srcmask2
.Fn CPU_OR &dstmask &srcmask1 srcmask2
.Fn CPU_XOR &dstmask &srcmask1 &srcmask2
.Fn CPU_EQUAL &mask1 &mask2
.Sh DESCRIPTION
.Pp
The
.Fn sched_setaffinity
sets the CPU affinity mask of the process,
which is identified by the
.Fa pid
to the value specified by the
.Fa mask .
The
.Fa cpusetsize
is the length (in bytes) of the data pointed to by
.Fa mask .
Normally this argument would be specified as sizeof(cpu_set_t).
If the
.Fa pid
is zero,
then the pid of the calling process is used.
All threads of the process identified by
.Fa pid
are affected.
If the calling thread is one of the target process's threads,
then the calling thread will be migrated immediately,
if necessary,
while other threads of the targt process will be migrated
by the scheduler later.
.Pp
A process created by
.Xr fork 2 ,
.Xr vfork 2 ,
and
.Xr rfork 2
inherits the calling thread's CPU affinity mask.
Same applies to the threads created by
.Xr lwp_create 2 ,
and the threads created by
.Xr pthread_create 3 .
.Pp
.Fn sched_getaffinity
writes the affinity mask of the process
identified by the
.Fa pid
to the cpu_set_t structure pointed to by
.Fa mask .
If the
.Fa pid
is zero,
then the pid of the calling process is used.
If the process is multithreaded,
then the CPU affinity mask of the first thread will be returned.
.Pp
The cpu_set_t data structure represents a set of CPUs.
The first available CPU on the system corresponds to a cpu value of 0,
the next CPU corresponds to a cpu value of 1,
and so on and so forth.
The constant
.Va CPU_SETSIZE
specifies a value one greater than the maximum
CPU number that can be stored in cpu_set_t.
The cpu_set_t should be treated as opaque data structure;
all manipulation of cpu_set_t should be done via the following macros:
.Bl -tag -width "CPU_COUNTxxx"
.It Fn CPU_ZERO
Reset the
.Fa mask ,
so that it contains no CPUs.
.It Fn CPU_SET
Add the
.Fa cpu
to the
.Fa mask .
.It Fn CPU_CLR
Remove the
.Fa cpu
from the
.Fa mask .
.It Fn CPU_ISSET
Test to see whether the
.Fa cpu
is a member of the
.Fa mask .
.It Fn CPU_COUNT
Return the number of CPUs in the
.Fa mask .
.It Fn CPU_AND
Store the intersection of the
.Fa srcmask1
and the
.Fa srcmask2
in the
.Fa dstmask .
The
.Fa dstmask
could be one of the source masks.
.It Fn CPU_OR
Store the union of the
.Fa srcmask1
and the
.Fa srcmask2
in the
.Fa dstmask .
The
.Fa dstmask
could be one of the source masks.
.It Fn CPU_XOR
Store the XOR of the
.Fa srcmask1
and the
.Fa srcmask2
in the
.Fa dstmask .
The
.Fa dstmask
could be one of the source masks.
.It Fn CPU_EQUAL
Test whether the
.Fa mask1
and the
.Fa mask2
contain the same CPUs.
.El
.Sh RETURN VALUES
These system calls return \-1 on error and
0 upon successful completion.
.Sh ERRORS
The
.Fn sched_setaffinity
and
.Fn sched_getaffinity
will fail if:
.Bl -tag -width Er
.It Bq Er EFAULT
The
.Fa mask
parameter is outside the process's allocated address space.
.It Bq Er EINVAL
The
.Fa pid
parameter is negative.
.It Bq Er ESRCH
The process identified by the
.Fa pid
does not exist.
.It Bq Er EPERM
The
.Fa mask
does not contain a valid CPU.
.El
.Sh SEE ALSO
.Xr fork 2
.Xr lwp_create 2
.Xr lwp_getaffinity 2
.Xr lwp_setaffinity 2
.Xr pthread_create 3
.Xr pthread_getaffinity_np 3
.Xr pthread_setaffinity_np 3
.Xr rfork 2
.Xr vfork 2
.Sh HISTORY
The
.Fn sched_setaffinity
and
.Fn sched_getaffinity
functions first appeared in
.Dx 4.7 .