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NetBSD 6.1.5 - man page for sched_4bsd (netbsd section 9)

SCHED_4BSD(9)			  BSD 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, 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-
     ority threads.

     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().

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.

BSD					  July 14, 2007 				      BSD


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