untrusted comment: verify with openbsd-66-base.pub
RWSvK/c+cFe24CxYjW+8VVH7seLUmOL9/IEH+YhcJ8EwelQpa4moJGz5HI1D6COggZp1nyYJ4ggE1w/pgg8PkZnZDL4NvWnxsgU=

OpenBSD 6.6 errata 035, July 22, 2020:

Only pty devices need reprint delays.

Apply by doing:
    signify -Vep /etc/signify/openbsd-66-base.pub -x 035_tty.patch.sig \
        -m - | (cd /usr/src && patch -p0)

And then rebuild and install a new kernel:
    KK=`sysctl -n kern.osversion | cut -d# -f1`
    cd /usr/src/sys/arch/`machine`/compile/$KK
    make obj
    make config
    make
    make install

Index: sys/kern/tty.c
===================================================================
RCS file: /cvs/src/sys/kern/tty.c,v
diff -u -p -u -r1.148.2.1 tty.c
--- sys/kern/tty.c	15 Jul 2020 21:55:31 -0000	1.148.2.1
+++ sys/kern/tty.c	20 Jul 2020 19:07:05 -0000
@@ -227,8 +227,8 @@ ttyclose(struct tty *tp)
 
 
 /*
- * Process input of a single character received on a tty.  Returns 0 for
- * simple operations, 1 for costly ones (ptcwrite needs to know).
+ * Process input of a single character received on a tty.  Returns 0 normally,
+ * 1 if a costly operation was reached.
  */
 int
 ttyinput(int c, struct tty *tp)
@@ -2005,11 +2005,7 @@ ttyretype(struct tty *tp)
 
 	tp->t_rocount = tp->t_rawq.c_cc;
 	tp->t_rocol = 0;
-	/*
-	 * Yield because of expense, or possible ptcwrite() injection flood.
-	 * Also check for interrupt, and return upwards.
-	 */
-	return tsleep_nsec(tp, TTIPRI | PCATCH, "ttyretype", 1);
+	return (1);
 }
 
 /*
Index: sys/kern/tty_pty.c
===================================================================
RCS file: /cvs/src/sys/kern/tty_pty.c,v
diff -u -p -u -r1.94.2.1 tty_pty.c
--- sys/kern/tty_pty.c	15 Jul 2020 21:55:31 -0000	1.94.2.1
+++ sys/kern/tty_pty.c	20 Jul 2020 14:34:27 -0000
@@ -564,7 +564,8 @@ again:
 				wakeup(&tp->t_rawq);
 				goto block;
 			}
-			if ((*linesw[tp->t_line].l_rint)(*cp++, tp) == EINTR)
+			if ((*linesw[tp->t_line].l_rint)(*cp++, tp) == 1 &&
+			    tsleep(tp, TTIPRI | PCATCH, "ttyretype", 1) == EINTR)
 				goto interrupt;
 			cnt++;
 			cc--;