Process scheduling

The model

kernel/core/core_sched.{c,h}: preemptive, priority-based with time-slice round-robin inside a priority level. Task control blocks carry state, priority, slices, and the saved frame; the context switch (arch/x86_64/arch_context_switch.S) is ABI-probe-verified (SysV 16-byte stack alignment at the dispatch call - BUG-0137).

Ticks

The PIT fires IRQ0 at 100 Hz: tick counter, g_boot_time_ms, the soft-timer wheel, and the scheduler's preemption all hang off it. sched, ps, nice, sleep, kill, spawn, multi are the user-facing commands.

Background tasks and the policy watchdog

Long-running work (g6_test &, spinners) runs as background tasks. The watchdog subsystem (kernel/core/core_watchdog.c) adds monitored slots: a task that must feed its slot and stops doing so is killed - with the reason logged - while the kernel itself stays alive. The hardware watchdogs (TCO/WDAT) protect the whole machine instead: see internals/watchdog.md.

Signals and processes

Ring-3 processes get signals through the syscall interface; the user test programs (run signal_test, run fork_test, run exec_test, run pipe_test, run select_test) demonstrate the full Unix-shaped process model: fork, exec, pipes, select, mmap.