diff --git a/lib/libc/sys/nanosleep.2 b/lib/libc/sys/nanosleep.2
index 19ffcf1b7026..eb75c4b1043b 100644
--- a/lib/libc/sys/nanosleep.2
+++ b/lib/libc/sys/nanosleep.2
@@ -1,200 +1,205 @@
 .\"	$NetBSD: nanosleep.2,v 1.23 2016/11/14 10:40:59 wiz Exp $
 .\"
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 .\"     @(#)sleep.3	8.1 (Berkeley) 6/4/93
 .\" $FreeBSD$
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-.Dd March 17, 2017
+.Dd October 7, 2021
 .Dt NANOSLEEP 2
 .Os
 .Sh NAME
 .Nm nanosleep
 .Nd high resolution sleep
 .Sh LIBRARY
 .Lb libc
 .Sh SYNOPSIS
 .In time.h
 .Ft int
 .Fo clock_nanosleep
 .Fa "clockid_t clock_id"
 .Fa "int flags"
 .Fa "const struct timespec *rqtp"
 .Fa "struct timespec *rmtp"
 .Fc
 .Ft int
 .Fo nanosleep
 .Fa "const struct timespec *rqtp"
 .Fa "struct timespec *rmtp"
 .Fc
 .Sh DESCRIPTION
 If the
 .Dv TIMER_ABSTIME
 flag is not set in the
 .Fa flags
 argument, then
 .Fn clock_nanosleep
 suspends execution of the calling thread until either the
 time interval specified by the
 .Fa rqtp
 argument has elapsed,
 or a signal is delivered to the calling process and its
 action is to invoke a signal-catching function or to terminate the
 process.
 The clock used to measure the time is specified by the
 .Fa clock_id
 argument.
 .Pp
 If the
 .Dv TIMER_ABSTIME
 flag is set in the
 .Fa flags
 argument, then
 .Fn clock_nanosleep
 suspends execution of the calling thread until either the value
 of the clock specified by the
 .Fa clock_id
 argument reaches the absolute time specified by the
 .Fa rqtp
 argument,
 or a signal is delivered to the calling process and its
 action is to invoke a signal-catching function or to terminate the
 process.
 If, at the time of the call, the time value specified by
 .Fa rqtp
 is less than or equal to the time value of the specified clock, then
 .Fn clock_nanosleep
 returns immediately and the calling thread is not suspended.
 .Pp
 The suspension time may be longer than requested due to the
 scheduling of other activity by the system.
+It is also subject to the allowed time interval deviation
+specified by the
+.Va kern.timecounter.alloweddeviation
+.Xr sysctl 8
+variable.
 An unmasked signal will terminate the sleep early, regardless of the
 .Dv SA_RESTART
 value on the interrupting signal.
 The
 .Fa rqtp
 and
 .Fa rmtp
 arguments can point to the same object.
 .Pp
 The following
 .Fa clock_id
 values are supported:
 .Pp
 .Bl -item -compact -offset indent
 .It
 CLOCK_MONOTONIC
 .It
 CLOCK_MONOTONIC_FAST
 .It
 CLOCK_MONOTONIC_PRECISE
 .It
 CLOCK_REALTIME
 .It
 CLOCK_REALTIME_FAST
 .It
 CLOCK_REALTIME_PRECISE
 .It
 CLOCK_SECOND
 .It
 CLOCK_UPTIME
 .It
 CLOCK_UPTIME_FAST
 .It
 CLOCK_UPTIME_PRECISE
 .El
 .Pp
 The
 .Fn nanosleep
 function behaves like
 .Fn clock_nanosleep
 with a
 .Fa clock_id
 argument of
 .Dv CLOCK_REALTIME
 and without the
 .Dv TIMER_ABSTIME
 flag in the
 .Fa flags
 argument.
 .Sh RETURN VALUES
 These functions return zero when the requested time has elapsed.
 .Pp
 If these functions return for any other reason, then
 .Fn clock_nanosleep
 will directly return the error number, and
 .Fn nanosleep
 will return \-1 with the global variable
 .Va errno
 set to indicate the error.
 If a relative sleep is interrupted by a signal and
 .Fa rmtp
 is
 .Pf non- Dv NULL ,
 the timespec structure it references is updated to contain the
 unslept amount (the request time minus the time actually slept).
 .Sh ERRORS
 These functions can fail with the following errors.
 .Bl -tag -width Er
 .It Bq Er EFAULT
 Either
 .Fa rqtp
 or
 .Fa rmtp
 points to memory that is not a valid part of the process
 address space.
 .It Bq Er EINTR
 The function was interrupted by the delivery of a signal.
 .It Bq Er EINVAL
 The
 .Fa rqtp
 argument specified a nanosecond value less than zero
 or greater than or equal to 1000 million.
 .It Bq Er EINVAL
 The
 .Fa flags
 argument contained an invalid flag.
 .It Bq Er EINVAL
 The
 .Fa clock_id
 argument was
 .Dv CLOCK_THREAD_CPUTIME_ID
 or an unrecognized value.
 .It Bq Er ENOTSUP
 The
 .Fa clock_id
 argument was valid but not supported by this implementation of
 .Fn clock_nanosleep .
 .El
 .Sh SEE ALSO
 .Xr clock_gettime 2 ,
 .Xr sigaction 2 ,
 .Xr sleep 3
 .Sh STANDARDS
 These functions conform to
 .St -p1003.1-2008 .