SCHED_4BSD(9) BSD Kernel Developer's Manual SCHED_4BSD(9)
sched_4bsd -- The 4.4BSD thread scheduler
sched_tick(struct cpu_info *ci);
sched_pstats_hook(struct proc *p, int minslp);
The traditional 4.4BSD scheduler employs a ``multilevel feedback queues'' algorithm, favour-
ing interactive, short-running threads to CPU-bound ones.
resetpriority() recomputes the priority of a thread running in user mode. If the resulting
priority is higher than that of the current thread, a reschedule is arranged.
sched_tick() gets called from hardclock(9) every 100ms to force a switch between equal pri-
The priority of the current thread is adjusted through sched_schedclock(). The priority of
a thread gets worse as it accumulates CPU time.
sched_pstats_hook() gets called from sched_pstats() every Hz ticks in order to recompute the
priorities of all threads.
sched_setrunnable() checks if an LWP has slept for more than one second. If so, its prior-
ity is updated by updatepri().
The 4.4BSD scheduler subsystem is implemented within the file sys/kern/sched_4bsd.c.
csf(9), hardclock(9), mi_switch(9), sched_m2(9), userret(9)
Marshall Kirk McKusick, Keith Bostic, Michael J. Karels, and John S. Quarterman, The Design
and Implementation of the 4.4BSD Operating System, Addison Wesley, 1996.
BSD July 14, 2007 BSD