Hi, On 2018-07-06, André Pribil <a.pribil@xxxxxxxxxxxx> wrote: > are there any plans to improve the latency with serial ttys and RT? > > I'm seeing very high latencies (up to 100 ms) when a high priority > RT thread accesses a serial tty port. I'm working with 4.14.52-rt34 > on a ARM system. As you later point out, this is a problem with the tty subsystem (kworker) and is not RT-specific. This problem needs to be fixed in mainline. > The reason for this issue seems to be that a kworker thread with a > normal priority is involved here. When the high priority RT > thread needs to wait for this kworker thread, it can easily be blocked > by other lower priority RT threads running in the system. > > I have seen that Steven Walter proposed some change in 2015, where > this kworker thread in replaced by a kthread with a RT priority if > the low_latency mode is selected. > See: https://www.spinics.net/lists/linux-serial/msg17782.html > > The follow-up discussion in this thread also proposes a solution that > allows low_latency ports to directly execute the worker. > As interrupts are already threaded in PREEMPT_RT, wouldn't that be a > solution? The patches and discussions in that thread provide some good ground work for a real solution. Someone needs to take more time to work with the maintainers to get it mainline. John Ogness -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
