table of contents
RUNQUEUE(9) | Kernel Developer's Manual | RUNQUEUE(9) |
NAME¶
chooseproc, procrunnable, remrunqueue, setrunqueue — manage the queue of runnable processesSYNOPSIS¶
#include <sys/param.h>#include <sys/proc.h> extern struct rq itqueues[];
extern struct rq rtqueues[];
extern struct rq queues[];
extern struct rq idqueues[]; struct thread *
choosethread(void); int
procrunnable(void); void
remrunqueue(struct thread *td); void
setrunqueue(struct thread *td);
DESCRIPTION¶
The run queue consists of four priority queues: itqueues for interrupt threads, rtqueues for realtime priority processes, queues for time sharing processes, and idqueues for idle priority processes. Each priority queue consists of an array ofNQS
queue header
structures. Each queue header identifies a list of runnable processes of equal
priority. Each queue also has a single word that contains a bit mask
identifying non-empty queues to assist in selecting a process quickly. These
are named itqueuebits,
rtqueuebits, queuebits, and
idqueuebits. The run queues are protected by the
sched_lock mutex.
procrunnable() returns zero if there are no runnable processes
other than the idle process. If there is at least one runnable process other
than the idle process, it will return a non-zero value. Note that the
sched_lock mutex does not need to be
held when this function is called. There is a small race window where one CPU
may place a process on the run queue when there are currently no other
runnable processes while another CPU is calling this function. In that case
the second CPU will simply travel through the idle loop one additional time
before noticing that there is a runnable process. This works because idle CPUs
are not halted in SMP systems. If idle CPUs are halted in SMP systems, then
this race condition might have more serious repercussions in the losing case,
and procrunnable() may have to require that the
sched_lock mutex be acquired.
choosethread() returns the highest priority runnable thread.
If there are no runnable threads, then the idle thread is returned. This
function is called by cpu_switch() and
cpu_throw() to determine which thread to switch to.
choosethread() must be called with the
sched_lock mutex held.
setrunqueue() adds the thread td to the
tail of the appropriate queue in the proper priority queue. The thread must be
runnable, i.e. p_stat must be set to
SRUN
. This function must be called with the
sched_lock mutex held.
remrunqueue() removes thread td from its
run queue. If td is not on a run queue, then the kernel
will panic(9). This function must be called with the
sched_lock mutex held.
SEE ALSO¶
cpu_switch(9), scheduler(9), sleepqueue(9)November 3, 2000 | Debian |