Boot Options

Below are kernel boot settings I've tried but didn't seem to have much affect.
I suspect some of them may be geared more towards different platforms such as intel.

No Difference / Makes things Worse

These are some of the settings that seem to be suggested but didn't seem to make any observable difference.
At least for a RPI4.

  • idle=poll
  • audit=0 Disable audit messages in dmesg
  • mitigations=off This disables certain security mitigations added to the kernel
  • plymouth.ignore-serial-consoles Don't issue a bootsplash on any serial console
  • rcu_nocbs=2,3 no difference
  • nohz_full=2,3 makes things worse I think

This option was used on the original linuxcnc image But it's not related to latency, instead it was to fix a USB issue with the older 5.4 kernels at the time

  • total_mem=3072

Scheduler

Historically one option to set would have been elevator=deadline.
However, this is now depreciated in more recent kernels.
The kernel will now automatically set a scheduler based on each device.
I suspect this is a setting we can leave alone for the newer kernels.

To see which ones are available for the sda device for example

cat /sys/block/sda/queue/scheduler
# Typically reports back
# none [mq-deadline] kyber bfq
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