|RUNQUEUE(9)||Kernel Developer's Manual||RUNQUEUE(9)|
extern struct rq itqueues;
extern struct rq rtqueues;
extern struct rq queues;
extern struct rq idqueues;
struct thread *
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 of
NQSqueue 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
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
This function must be called with the sched_lock mutex
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
SEE ALSO¶cpu_switch(9), scheduler(9), sleepqueue(9)
|August 15, 2010||Linux 4.19.0-10-amd64|