[LAU] realtime priority - FIFO vs Round Robin and scheduling

[Chris Caudle]

On Fri, May 27, 2016 12:45 pm, Ralf Mardorf wrote:
> if you're using a vanilla kernel, with boot option threadirqs
> proprietary drivers could be used.

In the past the kernel needed to be compiled with the CONFIG_PREEMPT flag
for threadirqs to be available.  I do not know if that is still true.

On Fedora at least the standard kernel does not use CONFIG_PREEMPT
(standard low latency) setting, it still uses CONFIG_PREEMPT_VOLUNTARY
which is less good for low latency use.

CONFIG_PREEMPT_VOLUNTARY=y
# CONFIG_PREEMPT is not set

Look at the kernel config in use, in order from worst to best the PREEMPT
options are:
CONFIG_PREEMPT_NONE          <- don't use this one
CONFIG_PREEMPT_VOLUNTARY  <-- not good for low latency
CONFIG_PREEMPT                    <- could be good for most use, test for
yourself
CONFIG_PREEMPT-RT           <- lowest latency, requires out of tree RT
patches


-- 
Chris Caudle