Ivo Sieben cee4ad1ed9
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 >
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cee4ad1ed9