On Thu, Sep 27, 2012 at 02:15:22PM +0100, Alan Cox wrote:

On Thu, 27 Sep 2012 13:58:21 +0200
Ivo Sieben [off-list ref] wrote:

quoted

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 <redacted>

Acked-by: Alan Cox <redacted>

(but for 3.8 not 3.7 ...)

Yes, I will hold onto this until 3.7-rc1 is out, thanks.

greg k-h