diff --git a/lib/libsys/Makefile.sys b/lib/libsys/Makefile.sys
--- a/lib/libsys/Makefile.sys
+++ b/lib/libsys/Makefile.sys
@@ -301,6 +301,7 @@
 	rtprio.2 \
 	sched_get_priority_max.2 \
 	sched_getcpu.3 \
+	sched_getaffinity.3 \
 	sched_setparam.2 \
 	sched_setscheduler.2 \
 	sched_yield.2 \
@@ -491,6 +492,7 @@
 	recv.2 recvmsg.2
 MLINKS+=rename.2 renameat.2
 MLINKS+=rtprio.2 rtprio_thread.2
+MLINKS+=sched_getaffinity.3 sched_setaffinity.3
 MLINKS+=sched_get_priority_max.2 sched_get_priority_min.2 \
 	sched_get_priority_max.2 sched_rr_get_interval.2
 MLINKS+=sched_setparam.2 sched_getparam.2
diff --git a/lib/libsys/sched_getaffinity.3 b/lib/libsys/sched_getaffinity.3
new file mode 100644
--- /dev/null
+++ b/lib/libsys/sched_getaffinity.3
@@ -0,0 +1,89 @@
+.\" SPDX-License-Identifier: BSD-2-Clause
+.\"
+.\" Copyright (c) 2025 Felix Johnson
+.Dd June 30, 2025
+.Dt SCHED_GETAFFINITY 3
+.Os
+.Sh NAME
+.Nm sched_getaffinity ,
+.Nm sched_setaffinity
+.Nd get or set thread to CPU affinity
+.Sh SYNOPSIS
+.Lb libc
+.Pp
+.In sched.h
+.Ft int
+.Fo sched_getaffinity
+.Fa "pid_t pid"
+.Fa "size_t cpusetsz"
+.Fa "cpuset_t *cpuset"
+.Fc
+.Pp
+.Ft int
+.Fo sched_setaffinity
+.Fa "pid_t pid"
+.Fa "size_t cpusetsz"
+.Fa "const cpuset_t *cpuset"
+.Fc
+.Sh DESCRIPTION
+These functions are convenience wrappers around
+.Xr cpuset_getaffinity 3
+and
+.Xr cpuset_setaffinity 3 .
+.Pp
+The
+.Fn sched_getaffinity
+function retrieves the current CPU affinity mask for
+a thread or process.
+If
+.Fa pid
+is 0, the calling thread is targeted.
+If
+.Fa pid
+is greater than 0, it refers to a process ID.
+In this case, the returned affinity mask is the union of
+the CPU masks of all threads within the specified process.
+.Pp
+The
+.Fn sched_setaffinity
+function sets the CPU affinity mask for a given thread,
+specifying which CPUs it is eligible to run on.
+If
+.Fa pid
+is 0, the calling thread is targeted.
+If
+.Fa pid
+is non-zero, it must be the thread ID of the target thread.
+This function does not affect all threads in a process;
+to change the affinity of all threads, the caller must
+set each thread's mask individually.
+.Pp
+Affinity masks are represented using the
+.Vt cpuset_t
+type, which encodes a set of CPUs as a bitmask.
+.Sh RETURN VALUES
+.Rv -std sched_getaffinity sched_setaffinity
+.Sh ERRORS
+See
+.Xr cpuset_getaffinity 3
+and
+.Xr cpuset_setaffinity 3
+for a list of possible error codes.
+.Sh SEE ALSO
+.Xr cpuset 2 ,
+.Xr cpuset_getaffinity 2 ,
+.Xr cpuset_setaffinity 2
+.Sh STANDARDS
+The
+.Fn sched_getaffinity
+and
+.Fn sched_setaffinity
+functions originated in Linux.
+This implementation aims to be source-compatible with the Linux implementation.
+.Sh HISTORY
+The
+.Fn sched_getaffinity
+and
+.Fn sched_setaffinity
+functions were introduced in
+.Fx 13.1 .