Solved unnecessary schedule latency in the TTY layer when used in
realtime context:
In case of PREEMPT_RT or when low_latency flag is set by the serial driver
the TTY receive flip buffer is copied to the line discipline directly
instead of using a workqueue in the background. Therefor only in case a
workqueue is actually used for copying data to the line discipline
we'll have to wait for the workqueue to finish. For a PREEMPT system this
prevents us from unnecessary blocking by the workqueue spin lock.
Note: In a PREEMPT_RT system "normal" spin locks behave like mutexes and
no interrupts (and therefor no scheduling) is disabled.
Signed-off-by: Ivo Sieben <meltedpianoman@xxxxxxxxx>
---
drivers/tty/tty_buffer.c | 18 +++++++++++-------
1 files changed, 11 insertions(+), 7 deletions(-)
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 6c9b7cd..ed86359 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -317,12 +317,7 @@ EXPORT_SYMBOL(tty_insert_flip_string_flags);
void tty_schedule_flip(struct tty_struct *tty)
{
- unsigned long flags;
- spin_lock_irqsave(&tty->buf.lock, flags);
- if (tty->buf.tail != NULL)
- tty->buf.tail->commit = tty->buf.tail->used;
- spin_unlock_irqrestore(&tty->buf.lock, flags);
- schedule_work(&tty->buf.work);
+ tty_flip_buffer_push(tty);
}
EXPORT_SYMBOL(tty_schedule_flip);
@@ -469,7 +464,16 @@ static void flush_to_ldisc(struct work_struct *work)
*/
void tty_flush_to_ldisc(struct tty_struct *tty)
{
- flush_work(&tty->buf.work);
+ /*
+ * Only in case a workqueue is actually used for copying data to the
+ * line discipline, we'll have to wait for the workqueue to finish. In
+ * other cases this prevents us from unnecessary blocking by the workqueue
+ * spin lock.
+ */
+#ifndef CONFIG_PREEMPT_RT_FULL
+ if (!tty->low_latency)
+ flush_work(&tty->buf.work);
+#endif
}
/**
--
1.7.0.4
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