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.Dd September 21, 2002
.Dt SETRUNQUEUE 9
.Os
.Sh NAME
.Nm setrunqueue ,
.Nm remrunqueue ,
.Nm nextrunqueue
.Nd manipulate system run queue
.Sh SYNOPSIS
.Fd #include \*[Lt]sys/proc.h\*[Gt]
.Fd #include \*[Lt]sys/sched.h\*[Gt]
.Ft void
.Fn setrunqueue "struct proc *p"
.Ft void
.Fn remrunqueue "struct proc *p"
.Ft struct proc *
.Fn nextrunqueue "void"
.Sh DESCRIPTION
The
.Fn setrunqueue ,
.Fn remrunqueue ,
and
.Fn nextrunqueue
functions manipulate the system queue of runnable processes.
The system scheduler uses this queue to find the highest-priority process
when a process switch occurs.
These functions are generally machine-dependent implementations in order
to permit efficient implementation of priority-based process selection.
.Pp
.Bf -symbolic
Currently, these functions are scheduler specific and correspond to
the default
.Dq time-sharing
scheduler in
.Nx .
Their implementation is likely to change in the future to cater for
different schedulers.
.Ef
.Pp
The priority queue consists of an array
.Va sched_qs[NQS]
of queue header structures each of which identifies a list of runnable
processes of equal priority.
Lower indices in
.Va sched_qs
indicate higher priority.
A single word
.Va sched_whichqs
containing a bit mask identifying non-empty queues assists in
selecting a process quickly.
The running process is on no queue, other processes are on a queue related
to p->p_priority, divided by 4 actually to shrink the 0-127 range of
priorities into the 32 available queues.
.Pp
The
.Fn setrunqueue
function places the given process on the system run queue.
It is an error to call
.Fn setrunqueue
with a process that is not runnable or that is already on the system
run queue or sleep queue.
.Pp
The
.Fn remrunqueue
function removes the given process from the system run queue.
It is an error to call
.Fn remrunqueue
with a process that is not on the system run queue.
.Pp
The
.Fn nextrunqueue
function will make a choice amongst the processes which are ready to
run from the priority run queue.
.Fn nextrunqueue
will remove the first process from the list on the queue with the
highest priority a return it.
.Pp
These functions must be called with the scheduler lock held
.Pq see Xr SCHED_LOCK 9
and at the
.Xr splsched 9
interrupt protection level,
.Sh SEE ALSO
.Xr SCHED_LOCK 9 ,
.Xr scheduler 9 ,
.Xr splsched 9