Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932404Ab3GWNPi (ORCPT ); Tue, 23 Jul 2013 09:15:38 -0400 Received: from mailout02.c08.mtsvc.net ([205.186.168.190]:47701 "EHLO mailout02.c08.mtsvc.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932148Ab3GWNPg (ORCPT ); Tue, 23 Jul 2013 09:15:36 -0400 X-Greylist: delayed 1660 seconds by postgrey-1.27 at vger.kernel.org; Tue, 23 Jul 2013 09:15:36 EDT From: Peter Hurley To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Jiri Slaby , Peter Hurley Subject: [PATCH v5 23/24] n_tty: Special case pty flow control Date: Tue, 23 Jul 2013 08:47:30 -0400 Message-Id: <1374583650-3853-1-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1371302076-4688-24-git-send-email-peter@hurleysoftware.com> References: <1371302076-4688-24-git-send-email-peter@hurleysoftware.com> X-Authenticated-User: 125194 peter@hurleysoftware.com Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2094 Lines: 59 The pty driver forces ldisc flow control on, regardless of available receive buffer space, so the writer can be woken whenever unthrottle is called. However, this 'forced throttle' has performance consequences, as multiple atomic operations are necessary to unthrottle and perform the write wakeup for every input line (in canonical mode). Instead, short-circuit the unthrottle if the tty is a pty and perform the write wakeup directly. Signed-off-by: Peter Hurley --- v5: fix regression in unusual pty/ldisc configurations where i/o fails to make forward progress drivers/tty/n_tty.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 0e3efc1..59eb444 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -231,6 +231,8 @@ static void n_tty_write_wakeup(struct tty_struct *tty) static inline void n_tty_check_throttle(struct tty_struct *tty) { + if (tty->driver->type == TTY_DRIVER_TYPE_PTY) + return; /* * Check the remaining room for the input canonicalization * mode. We don't want to throttle the driver if we're in @@ -250,6 +252,18 @@ static inline void n_tty_check_throttle(struct tty_struct *tty) static inline void n_tty_check_unthrottle(struct tty_struct *tty) { + if (tty->driver->type == TTY_DRIVER_TYPE_PTY && + tty->link->ldisc->ops->write_wakeup == n_tty_write_wakeup) { + if (chars_in_buffer(tty) > TTY_THRESHOLD_UNTHROTTLE) + return; + if (!tty->count) + return; + n_tty_set_room(tty); + n_tty_write_wakeup(tty->link); + wake_up_interruptible_poll(&tty->link->write_wait, POLLOUT); + return; + } + /* If there is enough space in the read buffer now, let the * low-level driver know. We use chars_in_buffer() to * check the buffer, as it now knows about canonical mode. -- 1.8.1.2 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/