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


NAME

     CSF -- The NetBSD common scheduler framework


SYNOPSIS

     #include <sys/sched.h>

     void
     sched_rqinit(void);

     void
     sched_setup(void);

     void
     sched_cpuattach(struct cpu_info *);

     void
     sched_tick(struct cpu_info *);

     void
     sched_schedclock(lwp_t *);

     bool
     sched_curcpu_runnable_p(void);

     lwp_t *
     sched_nextlwp(void);

     void
     sched_enqueue(lwp_t *, bool);

     void
     sched_dequeue(lwp_t *);

     void
     sched_nice(struct proc *, int);

     void
     sched_proc_fork(struct proc *, struct proc *);

     void
     sched_proc_exit(struct proc *, struct proc *);

     void
     sched_lwp_fork(lwp_t *);

     void
     sched_lwp_exit(lwp_t *);

     void
     sched_setrunnable(lwp_t *);

     void
     sched_print_runqueue(void (*pr)(const char *, ...));

     void
     sched_pstats_hook(struct proc *, int);

     void
     sched_pstats(void *arg);

     pri_t
     sched_kpri(lwp_t *);

     void
     resched_cpu(lwp_t *);

     void
     setrunnable();

     void
     schedclock(lwp_t *);

     void
     sched_init(void);


DESCRIPTION

     CSF provides a modular and self-contained interface for implementing dif-
     ferent thread scheduling algorithms.  The different schedulers can be
     selected at compile-time.  Currently, the schedulers available are
     sched_4bsd(9), the traditional 4.4BSD thread scheduler, and sched_m2(9)
     which implements a SVR4/Solaris like approach.

     The interface is divided into two parts: A set of functions each sched-
     uler needs to implement and common functions used by all schedulers.

Scheduler-specific functions
     The following functions have to be implemented by the individual sched-
     uler.

   Scheduler initialization
     void sched_cpuattach(struct cpu_info *)
              Per-CPU scheduler initialization routine.

     void sched_rqinit(void)
              Initialize the scheduler's runqueue data structures.

     void sched_setup(void)
              Setup initial scheduling parameters and kick off timeout driven
              events.

   Runqueue handling
     Runqueue handling is completely internal to the scheduler.  Other parts
     of the kernel should access runqueues only through the following func-
     tions:

     void sched_enqueue(lwp_t *, bool)
              Place an LWP within the scheduler's runqueue structures.

     void sched_dequeue(lwp_t *)
              Remove an LWP from the scheduler's runqueue structures.

     lwp_t * sched_nextlwp(void)
              Return the LWP that should run the CPU next.

     bool sched_curcpu_runnable_p(void)
              Indicate if there is a runnable LWP for the current CPU.

     void sched_print_runqueue(void (*pr)(const char *, ...))
              Print runqueues in DDB.

   Core scheduler functions
     void sched_tick(struct cpu_info *)
              Periodically called from hardclock(9).  Determines if a resched-
              ule is necessary, if the running LWP has used up its quantum.

     void sched_schedclock(lwp_t *)
              Periodically called from schedclock() in order to handle prior-
              ity adjustment.

   Priority adjustment
     void sched_nice(struct proc *, int)
              Recalculate the process priority according to its nice value.

   General helper functions
     void sched_proc_fork(struct proc *, struct proc *)
              Inherit the scheduling history of the parent process after
              fork().

     void sched_proc_exit(struct proc *, struct proc *)
              Charge back a processes parent for its resource usage.

     void sched_lwp_fork(lwp_t *)
              LWP-specific version of the above

     void sched_lwp_exit(lwp_t *)
              LWP-specific version of the above

     void sched_setrunnable(lwp_t *)
              Scheduler-specific actions for setrunnable().

     void sched_pstats_hook(struct proc *, int)
              Scheduler-specific actions for sched_pstats().

Common scheduler functions
     pri_t sched_kpri(lwp_t *)
              Scale a priority level to a kernel priority level, usually for
              an LWP that is about to sleep.

     void sched_pstats(void *)
              Update process statistics and check CPU resource allocation.

     inline void resched_cpu(lwp_t *)
              Arrange for a reschedule.

     void setrunnable(lwp_t *)
              Change process state to be runnable, placing it on a runqueue if
              it is in memory, awakening the swapper otherwise.

     void schedclock(lwp_t *)
              Scheduler clock.  Periodically called from statclock().

     void sched_init(void)
              Initialize callout for sched_pstats() and call sched_setup() to
              initialize any other scheduler-specific data.


CODE REFERENCES

     The CSF programming interface is defined within the file sys/sys/sched.h.

     Functions common to all scheduler implementations are in
     sys/kern/kern_synch.c.

     The traditional 4.4BSD scheduler is implemented in sys/kern/sched_4bsd.c.

     The M2 scheduler is implemented in sys/kern/sched_m2.c.


SEE ALSO

     mi_switch(9), preempt(9), sched_4bsd(9), sched_m2(9)


HISTORY

     The CSF appeared in NetBSD 5.0.


AUTHORS

     The CSF was written by Daniel Sieger <dsieger@NetBSD.org>.

NetBSD 8.2                     October 27, 2014                     NetBSD 8.2