Scheduling Model

The scheduling model

Written against 95d0321e, the 1.0.2 pin. This is the change most likely to surprise someone who read an older document: NebulaOS is not a PREEMPT_RT system any more.

The kernel is built with CONFIG_PREEMPT (nebulaos_halley5_v30_defconfig line 7), not CONFIG_PREEMPT_RT. The tree is still based on linux-stable-rt, so the RT patch set is present in the source and the model is one defconfig line to switch; localversion-rt was removed in 11f0f0c87 so a kernel that is not RT does not report -rt79 in uname.

Two consequences a developer should know:

• NEBULAOS_KTIMERS_PRIO is gone with it - ktimers/N threads only exist on RT.
• The IRQ thread priority table stays and still applies: MIPS selects IRQ_FORCED_THREADING, and the explicitly threaded handlers (uart1, DWC2, mmc) are threaded on PREEMPT too.