Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753052Ab3C0Lol (ORCPT ); Wed, 27 Mar 2013 07:44:41 -0400 Received: from mailout01.c08.mtsvc.net ([205.186.168.189]:54248 "EHLO mailout01.c08.mtsvc.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752672Ab3C0Loj (ORCPT ); Wed, 27 Mar 2013 07:44:39 -0400 From: Peter Hurley To: Greg Kroah-Hartman , Jiri Slaby Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Min Zhang , Ilya Zykov , Peter Hurley Subject: [PATCH v2 02/18] tty: Make ldisc input flow control concurrency-friendly Date: Wed, 27 Mar 2013 07:43:52 -0400 Message-Id: <1364384648-6636-3-git-send-email-peter@hurleysoftware.com> X-Mailer: git-send-email 1.8.1.2 In-Reply-To: <1364384648-6636-1-git-send-email-peter@hurleysoftware.com> References: <1363724513-15604-1-git-send-email-peter@hurleysoftware.com> <1364384648-6636-1-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: 6425 Lines: 209 Although line discipline receiving is single-producer/single-consumer, using tty->receive_room to manage flow control creates unnecessary critical regions requiring additional lock use. Instead, introduce the optional .receive_room() ldisc method which returns the maximum # of bytes the .receive_buf() ldisc method can accept. Serialization is guaranteed by the caller. In turn, the line discipline should schedule the buffer work item whenever space becomes available; ie., when there is room to receive data and receive_room() previously returned 0 (the buffer work item stops processing if receive_room() is 0). Add n_tty_receive_room() as the receive_room() method for N_TTY and remove tty->receive_room references in N_TTY. Line disciplines not using input flow control can continue to set tty->receive_room to a fixed value. Signed-off-by: Peter Hurley --- drivers/tty/n_tty.c | 68 ++++++++++++++++++++++++++++++----------------- drivers/tty/tty_buffer.c | 3 +++ include/linux/tty_ldisc.h | 8 ++++++ 3 files changed, 54 insertions(+), 25 deletions(-) diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c index 9b7f571..a185aff 100644 --- a/drivers/tty/n_tty.c +++ b/drivers/tty/n_tty.c @@ -74,11 +74,17 @@ #define ECHO_OP_SET_CANON_COL 0x81 #define ECHO_OP_ERASE_TAB 0x82 +/* Bit values for flags field + */ +#define NO_ROOM 0 + struct n_tty_data { unsigned int column; unsigned long overrun_time; int num_overrun; + unsigned long flags; + unsigned char lnext:1, erasing:1, raw:1, real_raw:1, icanon:1; unsigned char echo_overrun:1; @@ -114,25 +120,10 @@ static inline int tty_put_user(struct tty_struct *tty, unsigned char x, return put_user(x, ptr); } -/** - * n_tty_set_room - receive space - * @tty: terminal - * - * Updates tty->receive_room to reflect the currently available space - * in the input buffer, and re-schedules the flip buffer work if space - * just became available. - * - * Locks: Concurrent update is protected with read_lock - */ - -static int set_room(struct tty_struct *tty) +static ssize_t receive_room(struct tty_struct *tty) { struct n_tty_data *ldata = tty->disc_data; int left; - int old_left; - unsigned long flags; - - raw_spin_lock_irqsave(&ldata->read_lock, flags); if (I_PARMRK(tty)) { /* Multiply read_cnt by 3, since each byte might take up to @@ -150,18 +141,25 @@ static int set_room(struct tty_struct *tty) */ if (left <= 0) left = ldata->icanon && !ldata->canon_data; - old_left = tty->receive_room; - tty->receive_room = left; - - raw_spin_unlock_irqrestore(&ldata->read_lock, flags); - return left && !old_left; + return left; } +/** + * n_tty_set_room - receive space + * @tty: terminal + * + * Re-schedules the flip buffer work if space just became available. + * + * Locks: Concurrent update is protected with read_lock + */ + static void n_tty_set_room(struct tty_struct *tty) { + struct n_tty_data *ldata = tty->disc_data; + /* Did this open up the receive buffer? We may need to flip */ - if (set_room(tty)) { + if (receive_room(tty) && test_and_clear_bit(NO_ROOM, &ldata->flags)) { WARN_RATELIMIT(tty->port->itty == NULL, "scheduling with invalid itty\n"); /* see if ldisc has been killed - if so, this means that @@ -174,6 +172,27 @@ static void n_tty_set_room(struct tty_struct *tty) } } +/** + * n_tty_receive_room - receive space + * @tty: terminal + * + * Called by flush_to_ldisc() to determine the currently + * available space in the input buffer. + * + * Locks: Concurrent update is protected with read_lock + */ + +static ssize_t n_tty_receive_room(struct tty_struct *tty) +{ + struct n_tty_data *ldata = tty->disc_data; + + ssize_t room = receive_room(tty); + if (!room) + __set_bit(NO_ROOM, &ldata->flags); + + return room; +} + static void put_tty_queue_nolock(unsigned char c, struct n_tty_data *ldata) { if (ldata->read_cnt < N_TTY_BUF_SIZE) { @@ -1465,8 +1484,6 @@ static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp, tty->ops->flush_chars(tty); } - set_room(tty); - if ((!ldata->icanon && (ldata->read_cnt >= ldata->minimum_to_wake)) || L_EXTPROC(tty)) { kill_fasync(&tty->fasync, SIGIO, POLL_IN); @@ -1481,7 +1498,7 @@ static void n_tty_receive_buf(struct tty_struct *tty, const unsigned char *cp, */ while (1) { tty_set_flow_change(tty, TTY_THROTTLE_SAFE); - if (tty->receive_room >= TTY_THRESHOLD_THROTTLE) + if (receive_room(tty) >= TTY_THRESHOLD_THROTTLE) break; if (!tty_throttle_safe(tty)) break; @@ -2201,6 +2218,7 @@ struct tty_ldisc_ops tty_ldisc_N_TTY = { .receive_buf = n_tty_receive_buf, .write_wakeup = n_tty_write_wakeup, .fasync = n_tty_fasync, + .receive_room = n_tty_receive_room, }; /** diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index a42a028..f294631 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -449,6 +449,9 @@ static void flush_to_ldisc(struct work_struct *work) tty_buffer_free(port, head); continue; } + + if (disc->ops->receive_room) + tty->receive_room = disc->ops->receive_room(tty); if (!tty->receive_room) break; if (count > tty->receive_room) diff --git a/include/linux/tty_ldisc.h b/include/linux/tty_ldisc.h index 23bdd9d..6a8cb18 100644 --- a/include/linux/tty_ldisc.h +++ b/include/linux/tty_ldisc.h @@ -109,6 +109,13 @@ * * Tells the discipline that the DCD pin has changed its status. * Used exclusively by the N_PPS (Pulse-Per-Second) line discipline. + * + * ssize_t (*receive_room)(struct tty_struct *tty) + * + * If defined, returns the current # of bytes the receive_buf() + * method can accept. If not defined, this value is determined by + * the tty->receive_room value (which may be static if the line + * discipline does not perform flow control). */ #include @@ -195,6 +202,7 @@ struct tty_ldisc_ops { void (*write_wakeup)(struct tty_struct *); void (*dcd_change)(struct tty_struct *, unsigned int); void (*fasync)(struct tty_struct *tty, int on); + ssize_t (*receive_room)(struct tty_struct *tty); struct module *owner; -- 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/