Latency on UART when using Real Time priority threads

We are running the Linux kernel without Real Time (RT) patch(s). Our application software has a couple of threads using the POSIX RT priority levels and SCHED_FIFO. We have found that execution of these threads appears to block receiving of bytes on the UART, so there must be a lower priority thread in the system that handles the UART data receiving bytes. We want to avoid this extra latency on the UARTs… is there a simple way of doing so?
For example: If we just need to increase the priority of a particular thread in the system, which thread would be handling the UART drivers? If it’s not that simple, can the UART / TTY drivers in the kernel be modified to achieve this?

Hi @derrick.oem and Welcome to the Toradex Community!

The kernel 4.0.2 and Bsp 2.4 is not supported any more. Could you update to at least Bsp 2.8b6?

Best regards,