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SCHED_4BSD(9) NetBSD Kernel Developer's Manual SCHED_4BSD(9)
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by Kimmo Suominen.
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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, favouring interactive, short-running threads to CPU-bound
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 priority threads.
The priority of the current thread is adjusted through
sched_schedclock(). The priority of a thread gets worse as it accumu-
lates 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 priority is updated by updatepri().
To determine the scheduler currently in use
$ sysctl kern.sched.name
kern.sched.name = 4.4BSD
The 4.4BSD scheduler subsystem is implemented within the file
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.
NetBSD 9.99 April 9, 2019 NetBSD 9.99