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authorIvo Sieben <meltedpianoman@gmail.com>2012-09-27 14:02:05 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2012-10-22 16:47:51 -0700
commitcee4ad1ed90a0959fc29f9d30a2526e5e9522cfa (patch)
tree32b33be64fb490a9f7d3c704dea0a44ea3138ca6 /drivers
parentdaee779718a319ff9f83e1ba3339334ac650bb22 (diff)
tty: prevent unnecessary work queue lock checking on flip buffer copy
When low_latency flag is set the TTY receive flip buffer is copied to the line discipline directly instead of using a work queue in the background. Therefor only in case a workqueue is actually used for copying data to the line discipline we'll have to flush the workqueue. This prevents unnecessary spin lock/unlock on the workqueue spin lock that can cause additional scheduling overhead on a PREEMPT_RT system. On a 200 MHz AT91SAM9261 processor setup this fixes about 100us of scheduling overhead on the TTY read call. Signed-off-by: Ivo Sieben <meltedpianoman@gmail.com> Acked-by: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/tty/tty_buffer.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
index 91e326ffe7d..8b00f6a34a7 100644
--- a/drivers/tty/tty_buffer.c
+++ b/drivers/tty/tty_buffer.c
@@ -342,6 +342,8 @@ EXPORT_SYMBOL(tty_insert_flip_string_flags);
* Takes any pending buffers and transfers their ownership to the
* ldisc side of the queue. It then schedules those characters for
* processing by the line discipline.
+ * Note that this function can only be used when the low_latency flag
+ * is unset. Otherwise the workqueue won't be flushed.
*
* Locking: Takes tty->buf.lock
*/
@@ -514,7 +516,8 @@ static void flush_to_ldisc(struct work_struct *work)
*/
void tty_flush_to_ldisc(struct tty_struct *tty)
{
- flush_work(&tty->buf.work);
+ if (!tty->low_latency)
+ flush_work(&tty->buf.work);
}
/**