diff --git a/lib/libc/gen/Makefile.inc b/lib/libc/gen/Makefile.inc
--- a/lib/libc/gen/Makefile.inc
+++ b/lib/libc/gen/Makefile.inc
@@ -298,6 +298,7 @@
 	setjmp.3 \
 	setmode.3 \
 	setproctitle.3 \
+	sched_getaffinity.3 \
 	siginterrupt.3 \
 	signal.3 \
 	sigsetops.3 \
@@ -519,6 +520,7 @@
 	setjmp.3 sigsetjmp.3
 MLINKS+=setmode.3 getmode.3
 MLINKS+=setproctitle.3 setproctitle_fast.3
+MLINKS+=sched_getaffinity.3
 MLINKS+=sigsetops.3 sigaddset.3 \
 	sigsetops.3 sigandset.3 \
 	sigsetops.3 sigdelset.3 \
diff --git a/lib/libc/gen/sched_getaffinity.3 b/lib/libc/gen/sched_getaffinity.3
new file mode 100644
--- /dev/null
+++ b/lib/libc/gen/sched_getaffinity.3
@@ -0,0 +1,92 @@
+.\" 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
+.In sched.h
+.Ft int
+.Fo sched_getaffinity
+.Fa "pid_t pid"
+.Fa "size_t cpusetsz"
+.Fa "cpuset_t *cpuset"
+.Fc
+.Ft int
+.Fo sched_setaffinity
+.Fa "pid_t pid"
+.Fa "size_t cpusetsz"
+.Fa "const cpuset_t *cpuset"
+.Fc
+.Sh DESCRIPTION
+The
+.Fn sched_getaffinity
+function retrieves the current CPU affinity mask for
+a thread or process.
+.Pp
+The
+.Fn sched_setaffinity
+function sets the CPU affinity mask for a given thread
+or process, specifying which CPUs it is eligible to run on.
+.Pp
+The value of the
+.Fa pid
+parameter determines whether a thread or process is the target.
+If the value is 0,
+.Fa pid
+refers to the calling thread.
+If the value is greater than zero and less than or equal to
+.Dv PID_MAX ,
+.Fa pid
+refers to a process id.
+If the value is greater than
+.Dv PID_MAX ,
+then
+.Fa pid
+refers to a specific thread id.
+.Pp
+Getting the affinity mask for a process returns the union
+of CPUs available to the individual threads within the
+process.
+Setting the affinity mask for a process sets the affinity
+mask for all threads within the process.
+.Pp
+Affinity masks are represented using the
+.Vt cpuset_t
+type, which encodes a set of CPUs as a bitmask.
+.Pp
+These functions are convenience wrappers around
+.Xr cpuset_getaffinity 3
+and
+.Xr cpuset_setaffinity 3 .
+.Sh RETURN VALUES
+.Rv -std sched_getaffinity sched_setaffinity
+.Sh ERRORS
+See
+.Xr cpuset_getaffinity 2
+and
+.Xr cpuset_setaffinity 2
+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 .