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 different thread scheduling algorithms. The different schedulers can be selected at compile-time. Currently, the only scheduler available is sched_4bsd(9), the traditional 4.4BSD thread scheduler.

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

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

  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 functions:

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 reschedule is necessary, if the running LWP has used up its quantum.

void sched_schedclock(lwp_t *)
    Periodically called from schedclock() in order to handle priority 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
This section describes places within the NetBSD source tree where actual code implementing the scheduler can be found. All pathnames are relative to /usr/src.

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.

SEE ALSO
mi_switch(9), preempt(9), sched_4bsd(9)

HISTORY
The CSF appeared in NetBSD 5.0.

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