plan9fox/sys/man/9/sched

.TH SCHED 9
.SH NAME
anyhigher, anyready, hzsched, procpriority, procrestore, procsave, scheddump, schedinit, sched, yield
\- scheduler interactions
.SH SYNOPSIS
.ta \w'\fLchar* 'u +10n +8n +8n
.EX
int	anyhigher(void)
int	anyready(void)
void	hzsched(void)
void	procpriority(Proc *p, int priority, int fixed)
void	procrestore(Proc *p)
void	procsave(Proc *p)
void	procwired(Proc *p, int machno)
void	scheddump(void)
void	schedinit(void)
void	sched(void)
void	yield(void)

enum {
...
	Npriq		= 20,	/* scheduler priority levels */
	PriNormal	= 10,	/* base for normal processes */
	PriKproc	= 13,	/* base for kernel processes */
	PriRoot	= 13,	/* base for root processes */
};
.EE
.SH DESCRIPTION
.PP
These functions define the priority process scheduler's interface.
Processes are scheduled strictly by priority, and processor affinity.
When possible, processes with no affinity will be rescheduled on the
same processor.  Within a priority, scheduling is round–robin.
Long–running processes of the same priority are preempted and
rescheduled.  But cpu use (or lack thereof) may adjust the priority up
or down, unless it has been explicitly fixed.  Kernel processes are
started with
.B PriKproc
while user processes start with
.BR PriNormal .
.PP
.I Anyhigher
returns true if any higher priority processes are runnable, while
.I anyready
returns true if any processes are runnable at all.
.I Yield
gives up the processor and pretends to consume ½ clock tick, while
.I sched
invokes the scheduler, potentially recursively.
.I Sched
may be called outside process context.  Either may return immediately.
.I Schedinit
initializes scheduling on the running processor.
.PP
.I Procpriority
sets a process' priority directly.  Fixed–priority processes are not
reprioritized based on cpu use.
.I Procwired
makes a process runnable only on a single processor.
.PP
.I Hzsched
is called by the clock routine on every tick to collect statistics.
Periodically (typically once a second)
.I hzsched
reprioritizes based on cpu use.
.PP
.I Procsave
and
.I procrestore
are architecture–dependent routines used by the scheduler to save and
restore processes.
.I Scheddump
prints scheduler statistics.
.SH SOURCE
.B /sys/src/9/port/proc.c
.sp 0.3
.I Procsave
and
.I procrestore
can be found at
.br
.B /sys/src/9/*/main.c
.br
.B /sys/src/9/*/arch.c
.br
.B /sys/src/9/*/trap.c
.SH SEE ALSO
.IR edf (9),
.IR sleep (9)