From f23eb2b2b28547fc70df82dd5049eb39bec5ba12 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 22 Mar 2011 16:17:32 -0700 Subject: [PATCH] tty: stop using "delayed_work" in the tty layer Using delayed-work for tty flip buffers ends up causing us to wait for the next tick to complete some actions. That's usually not all that noticeable, but for certain latency-critical workloads it ends up being totally unacceptable. As an extreme case of this, passing a token back-and-forth over a pty will take two ticks per iteration, so even just a thousand iterations will take 8 seconds assuming a common 250Hz configuration. Avoiding the whole delayed work issue brings that ping-pong test-case down to 0.009s on my machine. In more practical terms, this latency has been a performance problem for things like dive computer simulators (simulating the serial interface using the ptys) and for other environments (Alan mentions a CP/M emulator). Reported-by: Jef Driesen Acked-by: Greg KH Acked-by: Alan Cox Signed-off-by: Linus Torvalds --- drivers/tty/tty_buffer.c | 14 +++++++------- drivers/tty/tty_ldisc.c | 14 +++++++------- include/linux/kbd_kern.h | 2 +- include/linux/tty.h | 2 +- 4 files changed, 16 insertions(+), 16 deletions(-) diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index d8210ca00720..b9451219528b 100644 --- a/drivers/tty/tty_buffer.c +++ b/drivers/tty/tty_buffer.c @@ -322,7 +322,7 @@ void tty_schedule_flip(struct tty_struct *tty) if (tty->buf.tail != NULL) tty->buf.tail->commit = tty->buf.tail->used; spin_unlock_irqrestore(&tty->buf.lock, flags); - schedule_delayed_work(&tty->buf.work, 1); + schedule_work(&tty->buf.work); } EXPORT_SYMBOL(tty_schedule_flip); @@ -402,7 +402,7 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags); static void flush_to_ldisc(struct work_struct *work) { struct tty_struct *tty = - container_of(work, struct tty_struct, buf.work.work); + container_of(work, struct tty_struct, buf.work); unsigned long flags; struct tty_ldisc *disc; @@ -443,7 +443,7 @@ static void flush_to_ldisc(struct work_struct *work) if (test_bit(TTY_FLUSHPENDING, &tty->flags)) break; if (!tty->receive_room || seen_tail) { - schedule_delayed_work(&tty->buf.work, 1); + schedule_work(&tty->buf.work); break; } if (count > tty->receive_room) @@ -481,7 +481,7 @@ static void flush_to_ldisc(struct work_struct *work) */ void tty_flush_to_ldisc(struct tty_struct *tty) { - flush_delayed_work(&tty->buf.work); + flush_work(&tty->buf.work); } /** @@ -506,9 +506,9 @@ void tty_flip_buffer_push(struct tty_struct *tty) spin_unlock_irqrestore(&tty->buf.lock, flags); if (tty->low_latency) - flush_to_ldisc(&tty->buf.work.work); + flush_to_ldisc(&tty->buf.work); else - schedule_delayed_work(&tty->buf.work, 1); + schedule_work(&tty->buf.work); } EXPORT_SYMBOL(tty_flip_buffer_push); @@ -529,6 +529,6 @@ void tty_buffer_init(struct tty_struct *tty) tty->buf.tail = NULL; tty->buf.free = NULL; tty->buf.memory_used = 0; - INIT_DELAYED_WORK(&tty->buf.work, flush_to_ldisc); + INIT_WORK(&tty->buf.work, flush_to_ldisc); } diff --git a/drivers/tty/tty_ldisc.c b/drivers/tty/tty_ldisc.c index 0fc564a97706..e19e13647116 100644 --- a/drivers/tty/tty_ldisc.c +++ b/drivers/tty/tty_ldisc.c @@ -529,7 +529,7 @@ static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old) static int tty_ldisc_halt(struct tty_struct *tty) { clear_bit(TTY_LDISC, &tty->flags); - return cancel_delayed_work_sync(&tty->buf.work); + return cancel_work_sync(&tty->buf.work); } /** @@ -542,7 +542,7 @@ static void tty_ldisc_flush_works(struct tty_struct *tty) { flush_work_sync(&tty->hangup_work); flush_work_sync(&tty->SAK_work); - flush_delayed_work_sync(&tty->buf.work); + flush_work_sync(&tty->buf.work); } /** @@ -722,9 +722,9 @@ enable: /* Restart the work queue in case no characters kick it off. Safe if already running */ if (work) - schedule_delayed_work(&tty->buf.work, 1); + schedule_work(&tty->buf.work); if (o_work) - schedule_delayed_work(&o_tty->buf.work, 1); + schedule_work(&o_tty->buf.work); mutex_unlock(&tty->ldisc_mutex); tty_unlock(); return retval; @@ -830,12 +830,12 @@ void tty_ldisc_hangup(struct tty_struct *tty) /* * this is like tty_ldisc_halt, but we need to give up - * the BTM before calling cancel_delayed_work_sync, - * which may need to wait for another function taking the BTM + * the BTM before calling cancel_work_sync, which may + * need to wait for another function taking the BTM */ clear_bit(TTY_LDISC, &tty->flags); tty_unlock(); - cancel_delayed_work_sync(&tty->buf.work); + cancel_work_sync(&tty->buf.work); mutex_unlock(&tty->ldisc_mutex); tty_lock(); diff --git a/include/linux/kbd_kern.h b/include/linux/kbd_kern.h index 4b0761cc7dd9..ec2d17bc1f1e 100644 --- a/include/linux/kbd_kern.h +++ b/include/linux/kbd_kern.h @@ -159,7 +159,7 @@ static inline void con_schedule_flip(struct tty_struct *t) if (t->buf.tail != NULL) t->buf.tail->commit = t->buf.tail->used; spin_unlock_irqrestore(&t->buf.lock, flags); - schedule_delayed_work(&t->buf.work, 0); + schedule_work(&t->buf.work); } #endif diff --git a/include/linux/tty.h b/include/linux/tty.h index 4e53d4641b38..9f469c700550 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -82,7 +82,7 @@ struct tty_buffer { struct tty_bufhead { - struct delayed_work work; + struct work_struct work; spinlock_t lock; struct tty_buffer *head; /* Queue head */ struct tty_buffer *tail; /* Active buffer */