At one point there was a flag in the tty_port structure (low_latency) that, if set, would push data to the tty ldisc immediately from hardirq context, instead of from the workqueue. That low latency support has not worked for some time, though the low_latency flag remains. Lacking any low latency mechanism for UART drivers makes their use in embedded systems with real-time threads tricky. Since workqueues run as a normal priority process, they can be easily starved by medium priority real-time threads, even when a higher-priority thread is waiting to read from the UART. This patch set provides a solution by deferring tty work to a kthread worker, instead of a workqueue. kthread workers run on dedicated kernel threads that can have a custom priority. Now, when port->low_latency is set, flush_to_ldisc will run on a dedicated real-time thread. The priority of that kernel thread can be changed at run-time so that real-time threads that read from the UART cannot be starved. -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
