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| author | Ivo Sieben <meltedpianoman@gmail.com> | 2012-09-27 14:02:05 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-10-22 16:47:51 -0700 |
| commit | cee4ad1ed90a0959fc29f9d30a2526e5e9522cfa (patch) | |
| tree | 32b33be64fb490a9f7d3c704dea0a44ea3138ca6 /drivers/tty/tty_buffer.c | |
| parent | daee779718a319ff9f83e1ba3339334ac650bb22 (diff) | |
| download | lwn-cee4ad1ed90a0959fc29f9d30a2526e5e9522cfa.tar.gz lwn-cee4ad1ed90a0959fc29f9d30a2526e5e9522cfa.zip | |
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/tty/tty_buffer.c')
| -rw-r--r-- | drivers/tty/tty_buffer.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c index 91e326ffe7db..8b00f6a34a7d 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); } /** |