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 <jefdriesen@telenet.be> Acked-by: Greg KH <gregkh@suse.de> Acked-by: Alan Cox <alan@lxorguk.ukuu.org.uk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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@ -322,7 +322,7 @@ void tty_schedule_flip(struct tty_struct *tty)
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if (tty->buf.tail != NULL)
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tty->buf.tail->commit = tty->buf.tail->used;
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spin_unlock_irqrestore(&tty->buf.lock, flags);
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schedule_delayed_work(&tty->buf.work, 1);
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schedule_work(&tty->buf.work);
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}
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EXPORT_SYMBOL(tty_schedule_flip);
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@ -402,7 +402,7 @@ EXPORT_SYMBOL_GPL(tty_prepare_flip_string_flags);
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static void flush_to_ldisc(struct work_struct *work)
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{
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struct tty_struct *tty =
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container_of(work, struct tty_struct, buf.work.work);
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container_of(work, struct tty_struct, buf.work);
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unsigned long flags;
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struct tty_ldisc *disc;
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@ -443,7 +443,7 @@ static void flush_to_ldisc(struct work_struct *work)
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if (test_bit(TTY_FLUSHPENDING, &tty->flags))
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break;
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if (!tty->receive_room || seen_tail) {
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schedule_delayed_work(&tty->buf.work, 1);
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schedule_work(&tty->buf.work);
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break;
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}
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if (count > tty->receive_room)
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@ -481,7 +481,7 @@ static void flush_to_ldisc(struct work_struct *work)
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*/
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void tty_flush_to_ldisc(struct tty_struct *tty)
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{
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flush_delayed_work(&tty->buf.work);
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flush_work(&tty->buf.work);
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}
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/**
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@ -506,9 +506,9 @@ void tty_flip_buffer_push(struct tty_struct *tty)
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spin_unlock_irqrestore(&tty->buf.lock, flags);
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if (tty->low_latency)
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flush_to_ldisc(&tty->buf.work.work);
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flush_to_ldisc(&tty->buf.work);
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else
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schedule_delayed_work(&tty->buf.work, 1);
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schedule_work(&tty->buf.work);
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}
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EXPORT_SYMBOL(tty_flip_buffer_push);
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@ -529,6 +529,6 @@ void tty_buffer_init(struct tty_struct *tty)
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tty->buf.tail = NULL;
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tty->buf.free = NULL;
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tty->buf.memory_used = 0;
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INIT_DELAYED_WORK(&tty->buf.work, flush_to_ldisc);
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INIT_WORK(&tty->buf.work, flush_to_ldisc);
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}
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@ -529,7 +529,7 @@ static void tty_ldisc_restore(struct tty_struct *tty, struct tty_ldisc *old)
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static int tty_ldisc_halt(struct tty_struct *tty)
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{
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clear_bit(TTY_LDISC, &tty->flags);
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return cancel_delayed_work_sync(&tty->buf.work);
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return cancel_work_sync(&tty->buf.work);
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}
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/**
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@ -542,7 +542,7 @@ static void tty_ldisc_flush_works(struct tty_struct *tty)
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{
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flush_work_sync(&tty->hangup_work);
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flush_work_sync(&tty->SAK_work);
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flush_delayed_work_sync(&tty->buf.work);
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flush_work_sync(&tty->buf.work);
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}
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/**
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@ -722,9 +722,9 @@ enable:
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/* Restart the work queue in case no characters kick it off. Safe if
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already running */
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if (work)
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schedule_delayed_work(&tty->buf.work, 1);
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schedule_work(&tty->buf.work);
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if (o_work)
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schedule_delayed_work(&o_tty->buf.work, 1);
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schedule_work(&o_tty->buf.work);
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mutex_unlock(&tty->ldisc_mutex);
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tty_unlock();
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return retval;
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@ -830,12 +830,12 @@ void tty_ldisc_hangup(struct tty_struct *tty)
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/*
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* this is like tty_ldisc_halt, but we need to give up
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* the BTM before calling cancel_delayed_work_sync,
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* which may need to wait for another function taking the BTM
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* the BTM before calling cancel_work_sync, which may
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* need to wait for another function taking the BTM
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*/
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clear_bit(TTY_LDISC, &tty->flags);
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tty_unlock();
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cancel_delayed_work_sync(&tty->buf.work);
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cancel_work_sync(&tty->buf.work);
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mutex_unlock(&tty->ldisc_mutex);
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tty_lock();
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@ -159,7 +159,7 @@ static inline void con_schedule_flip(struct tty_struct *t)
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if (t->buf.tail != NULL)
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t->buf.tail->commit = t->buf.tail->used;
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spin_unlock_irqrestore(&t->buf.lock, flags);
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schedule_delayed_work(&t->buf.work, 0);
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schedule_work(&t->buf.work);
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}
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#endif
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@ -82,7 +82,7 @@ struct tty_buffer {
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struct tty_bufhead {
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struct delayed_work work;
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struct work_struct work;
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spinlock_t lock;
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struct tty_buffer *head; /* Queue head */
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struct tty_buffer *tail; /* Active buffer */
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