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authorPeter Hurley <peter@hurleysoftware.com>2015-01-16 23:05:34 +0300
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-02-02 21:11:26 +0300
commit2c5dc4641ca0e046b432f94f7058c4aff3440e47 (patch)
tree7761dc343a76521f50742234aa996314f2060a32 /drivers/tty/n_tty.c
parent62d38099bf9dd0bdb582369b3cd049b67a0f1ac1 (diff)
downloadlinux-2c5dc4641ca0e046b432f94f7058c4aff3440e47.tar.xz
n_tty: Eliminate receive_room() from consumer/exclusive paths
The input worker never reschedules itself; it only processes input until either there is no more input or the read buffer is full. So the reader is responsible for restarting the input worker only if the read buffer was previously full (no_room == 1) _and_ space is now available to process more input because the reader has consumed data from the read buffer. However, computing the actual space available is not required to determine if the reader has consumed data from the read buffer. This condition is evaluated in 5 situations, each of which the space avail is already known: 1. n_tty_flush_buffer() - the read buffer is empty; kick the worker 2. n_tty_set_termios() - no data has been consumed; do not kick the worker (although it may have kicked the reader so data _will be_ consumed) 3. n_tty_check_unthrottle - avail space > 3968; kick the worker 4. n_tty_read, before leaving - only kick the worker if the reader has moved the tail. This prevents unnecessarily kicking the worker when timeout-style reading is used. 5. n_tty_read, before sleeping - although it is possible for the read buffer to be full and input_available_p() to be false, this can only happen when the input worker is racing the reader, in which case the reader will have been woken and won't sleep. Rename n_tty_set_room() to n_tty_kick_worker() to reflect what the function actually does. Signed-off-by: Peter Hurley <peter@hurleysoftware.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty/n_tty.c')
-rw-r--r--drivers/tty/n_tty.c23
1 files changed, 12 insertions, 11 deletions
diff --git a/drivers/tty/n_tty.c b/drivers/tty/n_tty.c
index 4ddfa60c9222..b60b043f47d8 100644
--- a/drivers/tty/n_tty.c
+++ b/drivers/tty/n_tty.c
@@ -187,10 +187,10 @@ static int receive_room(struct tty_struct *tty)
}
/**
- * n_tty_set_room - receive space
+ * n_tty_kick_worker - start input worker (if required)
* @tty: terminal
*
- * Re-schedules the flip buffer work if space just became available.
+ * Re-schedules the flip buffer work if it may have stopped
*
* Caller holds exclusive termios_rwsem
* or
@@ -198,12 +198,12 @@ static int receive_room(struct tty_struct *tty)
* holds non-exclusive termios_rwsem
*/
-static void n_tty_set_room(struct tty_struct *tty)
+static void n_tty_kick_worker(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 (unlikely(ldata->no_room) && receive_room(tty)) {
+ /* Did the input worker stop? Restart it */
+ if (unlikely(ldata->no_room)) {
ldata->no_room = 0;
WARN_RATELIMIT(tty->port->itty == NULL,
@@ -274,7 +274,7 @@ static void n_tty_check_unthrottle(struct tty_struct *tty)
return;
if (!tty->count)
return;
- n_tty_set_room(tty);
+ n_tty_kick_worker(tty);
n_tty_write_wakeup(tty->link);
if (waitqueue_active(&tty->link->write_wait))
wake_up_interruptible_poll(&tty->link->write_wait, POLLOUT);
@@ -296,7 +296,7 @@ static void n_tty_check_unthrottle(struct tty_struct *tty)
break;
if (!tty->count)
break;
- n_tty_set_room(tty);
+ n_tty_kick_worker(tty);
unthrottled = tty_unthrottle_safe(tty);
if (!unthrottled)
break;
@@ -379,7 +379,7 @@ static void n_tty_flush_buffer(struct tty_struct *tty)
{
down_write(&tty->termios_rwsem);
reset_buffer_flags(tty->disc_data);
- n_tty_set_room(tty);
+ n_tty_kick_worker(tty);
if (tty->link)
n_tty_packet_mode_flush(tty);
@@ -1817,7 +1817,6 @@ static void n_tty_set_termios(struct tty_struct *tty, struct ktermios *old)
else
ldata->real_raw = 0;
}
- n_tty_set_room(tty);
/*
* Fix tty hang when I_IXON(tty) is cleared, but the tty
* been stopped by STOP_CHAR(tty) before it.
@@ -2130,6 +2129,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
ssize_t retval = 0;
long timeout;
int packet;
+ size_t tail;
c = job_control(tty, file);
if (c < 0)
@@ -2166,6 +2166,7 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
}
packet = tty->packet;
+ tail = ldata->read_tail;
add_wait_queue(&tty->read_wait, &wait);
while (nr) {
@@ -2208,7 +2209,6 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
retval = -ERESTARTSYS;
break;
}
- n_tty_set_room(tty);
up_read(&tty->termios_rwsem);
timeout = wait_woken(&wait, TASK_INTERRUPTIBLE,
@@ -2253,7 +2253,8 @@ static ssize_t n_tty_read(struct tty_struct *tty, struct file *file,
if (time)
timeout = time;
}
- n_tty_set_room(tty);
+ if (tail != ldata->read_tail)
+ n_tty_kick_worker(tty);
up_read(&tty->termios_rwsem);
remove_wait_queue(&tty->read_wait, &wait);