sched_4bsd(9) - NetBSD Manual Pages

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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