Use dcdwait to block threads to serialize writes.

I suspect the usage of bgwait causes a lot of spurious wakeups when
threads are blocked in the background, because they will be woken up
each time a write() call is performed.

Also wakeup dcdwait when the TTY is abandoned.

1 files changed, 3 insertions, 2 deletions

diff --git a/sys/kern/tty.c b/sys/kern/tty.c
index 61c8785..4b2ce14 100644
--- a/sys/kern/tty.c
+++ b/sys/kern/tty.c
@@ -335,6 +335,7 @@ ttydev_close(struct cdev *dev, int fflag, int devtype, struct thread *td)
 	tp->t_revokecnt++;
 	tty_wakeup(tp, FREAD|FWRITE);
 	cv_broadcast(&tp->t_bgwait);
+	cv_broadcast(&tp->t_dcdwait);
 
 	ttydev_leave(tp);
 
@@ -455,7 +456,7 @@ ttydev_write(struct cdev *dev, struct uio *uio, int ioflag)
 	} else {
 		/* Serialize write() calls. */
 		while (tp->t_flags & TF_BUSY_OUT) {
-			error = tty_wait(tp, &tp->t_bgwait);
+			error = tty_wait(tp, &tp->t_dcdwait);
 			if (error)
 				goto done;
 		}
@@ -463,7 +464,7 @@ ttydev_write(struct cdev *dev, struct uio *uio, int ioflag)
  		tp->t_flags |= TF_BUSY_OUT;
 		error = ttydisc_write(tp, uio, ioflag);
  		tp->t_flags &= ~TF_BUSY_OUT;
-		cv_broadcast(&tp->t_bgwait);
+		cv_broadcast(&tp->t_dcdwait);
 	}
 
 done:	tty_unlock(tp);