sched_4bsd(9)
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SCHED_4BSD(9) NetBSD Kernel Developer's Manual SCHED_4BSD(9)
NAME
sched_4bsd -- The 4.4BSD thread scheduler
SYNOPSIS
#include <sys/sched.h>
void
resetpriority(lwp_t *l);
void
sched_tick(struct cpu_info *ci);
void
sched_schedclock(lwp_t *l);
void
sched_pstats_hook(struct proc *p, int minslp);
void
sched_setrunnable(lwp_t *l);
void
updatepri(lwp_t *l);
DESCRIPTION
The traditional 4.4BSD scheduler employs a ``multilevel feedback queues''
algorithm, favouring 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 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().
EXAMPLES
To determine the scheduler currently in use
$ sysctl kern.sched.name
kern.sched.name = 4.4BSD
CODE REFERENCES
The 4.4BSD scheduler subsystem is implemented within the file
sys/kern/sched_4bsd.c.
SEE ALSO
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 9.4_STABLE April 9, 2019 NetBSD 9.4_STABLE
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