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Extract the next runnable process selection out of cpu_switch() into a

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fairly machine independent C routine.  gcc actually does a pretty good
job of this.

Reviewed by:	msmith (in principle)
This commit is contained in:
Peter Wemm 1999-08-19 00:06:53 +00:00
parent 4b31e9d6a7
commit dba6c5a6f9
2 changed files with 205 additions and 0 deletions
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sys/conf/files
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@ -293,6 +293,7 @@ kern/kern_resource.c standard
kern/kern_shutdown.c standard
kern/kern_sig.c standard
kern/kern_subr.c standard
kern/kern_switch.c standard
kern/kern_synch.c standard
kern/kern_syscalls.c standard
kern/kern_sysctl.c standard

204
sys/kern/kern_switch.c Normal file
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@ -0,0 +1,204 @@
/*
* Copyright (c) 1999 Peter Wemm <peter@FreeBSD.org>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/proc.h>
#include <sys/rtprio.h>
#include <sys/queue.h>
/*
* We have NQS (32) run queues per scheduling class. For the normal
* class, there are 128 priorities scaled onto these 32 queues. New
* processes are added to the last entry in each queue, and processes
* are selected for running by taking them from the head and maintaining
* a simple FIFO arrangement. Realtime and Idle priority processes have
* and explicit 0-31 priority which maps directly onto their class queue
* index. When a queue has something in it, the corresponding bit is
* set in the queuebits variable, allowing a single read to determine
* the state of all 32 queues and then a ffs() to find the first busy
* queue.
*/
struct rq queues[NQS];
struct rq rtqueues[NQS];
struct rq idqueues[NQS];
u_int32_t queuebits;
u_int32_t rtqueuebits;
u_int32_t idqueuebits;
/*
* Initialize the run queues at boot time.
*/
static void
rqinit(void *dummy)
{
int i;
for (i = 0; i < NQS; i++) {
TAILQ_INIT(&queues[i]);
TAILQ_INIT(&rtqueues[i]);
TAILQ_INIT(&idqueues[i]);
}
}
SYSINIT(runqueue, SI_SUB_RUN_QUEUE, SI_ORDER_FIRST, rqinit, NULL)
/*
* setrunqueue() examines a process priority and class and inserts it on
* the tail of it's appropriate run queue (based on class and priority).
* This sets the queue busy bit.
* The process must be runnable.
* This must be called at splhigh().
*/
void
setrunqueue(struct proc *p)
{
struct rq *q;
u_int8_t pri;
KASSERT(p->p_stat == SRUN, ("setrunqueue: proc not SRUN"));
if (p->p_rtprio.type == RTP_PRIO_REALTIME) {
pri = p->p_rtprio.prio;
q = &rtqueues[pri];
rtqueuebits |= 1 << pri;
} else if (p->p_rtprio.type == RTP_PRIO_NORMAL) {
pri = p->p_priority >> 2;
q = &queues[pri];
queuebits |= 1 << pri;
} else if (p->p_rtprio.type == RTP_PRIO_IDLE) {
pri = p->p_rtprio.prio;
q = &idqueues[pri];
idqueuebits |= 1 << pri;
} else {
panic("setrunqueue: invalid rtprio type");
}
p->p_rqindex = pri; /* remember the queue index */
TAILQ_INSERT_TAIL(q, p, p_procq);
}
/*
* remrunqueue() removes a given process from the run queue that it is on,
* clearing the queue busy bit if it becomes empty.
* This must be called at splhigh().
*/
void
remrunqueue(struct proc *p)
{
struct rq *q;
u_int32_t *which;
u_int8_t pri;
pri = p->p_rqindex;
if (p->p_rtprio.type == RTP_PRIO_REALTIME) {
q = &rtqueues[pri];
which = &rtqueuebits;
} else if (p->p_rtprio.type == RTP_PRIO_NORMAL) {
q = &queues[pri];
which = &queuebits;
} else if (p->p_rtprio.type == RTP_PRIO_REALTIME) {
q = &idqueues[pri];
which = &idqueuebits;
} else {
panic("remrunqueue: invalid rtprio type");
}
TAILQ_REMOVE(q, p, p_procq);
if (TAILQ_EMPTY(q)) {
KASSERT((*which & (1 << pri)) != 0,
("remrunqueue: remove from empty queue"));
*which &= ~(1 << pri);
}
}
/*
* procrunnable() returns a boolean true (non-zero) value if there are
* any runnable processes. This is intended to be called from the idle
* loop to avoid the more expensive (and destructive) chooseproc().
*/
u_int32_t
procrunnable(void)
{
return (rtqueuebits || queuebits || idqueuebits);
}
/*
* chooseproc() selects the next process to run. Ideally, cpu_switch()
* would have determined that there is a process available before calling
* this, but it is not a requirement. The selected process is removed
* from it's queue, and the queue busy bit is cleared if it becomes empty.
* This must be called at splhigh().
*
* For SMP, trivial affinity is implemented by locating the first process
* on the queue that has a matching lastcpu id. Since normal priorities
* are mapped four priority levels per queue, this may allow the cpu to
* choose a slightly lower priority process in order to preserve the cpu
* caches.
*/
struct proc *
chooseproc(void)
{
struct proc *p;
struct rq *q;
u_int32_t *which;
u_int32_t pri;
#ifdef SMP
u_char id;
#endif
if (rtqueuebits) {
pri = ffs(rtqueuebits) - 1;
q = &rtqueues[pri];
which = &rtqueuebits;
} else if (queuebits) {
pri = ffs(queuebits) - 1;
q = &queues[pri];
which = &queuebits;
} else if (idqueuebits) {
pri = ffs(idqueuebits) - 1;
q = &idqueues[pri];
which = &idqueuebits;
} else {
return NULL;
}
p = TAILQ_FIRST(q);
KASSERT(p, ("chooseproc: no proc on busy queue"));
#ifdef SMP
/* wander down the current run queue for this pri level for a match */
id = cpuid;
while (p->p_lastcpu != id) {
p = TAILQ_NEXT(p, p_procq);
if (p == NULL) {
p = TAILQ_FIRST(q);
break;
}
}
#endif
TAILQ_REMOVE(q, p, p_procq);
if (TAILQ_EMPTY(q))
*which &= ~(1 << pri);
return p;
}