CSF(9) | 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 different 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 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

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⟩.

October 27, 2014 | NetBSD 9.2