sched_4bsd(9) - NetBSD Manual Pages

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SCHED_4BSD(9)          NetBSD Kernel Developer's Manual          SCHED_4BSD(9)

sched_4bsd -- The 4.4BSD thread scheduler
#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);
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().
To determine the scheduler currently in use $ sysctl = 4.4BSD
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. NetBSD 9.0 April 9, 2019 NetBSD 9.0
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