Date: Sun, 31 Jan 1999 06:33:40 -0500 (EST) From: Peter Dufault <dufault@hda.com> To: bde@zeta.org.au (Bruce Evans) Cc: current@FreeBSD.ORG, dufault@hda.com, bde@zeta.org.au Subject: Re: more about yield() versus sched_yield() Message-ID: <199901311133.GAA21441@hda.hda.com> In-Reply-To: <199901311057.VAA08719@godzilla.zeta.org.au> from Bruce Evans at "Jan 31, 99 09:57:07 pm"
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> Another difference is that it correctly counts context switches as voluntary.
Good point. The patched version calls maybe_resched(), and I'm
adding the line at "<<<".
(This also will let people who haven't looked at that code
complain about the function interface - it doesn't bother me,
macros could come later.)
/*
* prioritize: Compute a priority based on the type of scheduler.
*/
static priority_type
prioritize(struct proc *p)
{
priority_type priority;
int class = RTP_PRIO_BASE(p->p_rtprio.type);
if (class == RTP_PRIO_NORMAL) {
priority = (RTP_PRIO_NORMAL << 8) | (p->p_priority / PPQ);
}
else
priority = (class << 8) | p->p_rtprio.prio;
return priority;
}
/*
* curpriority_set: Set the current process priority to that of the process
* in the call.
*/
void
curpriority_set(struct proc *p)
{
newcurpriority = prioritize(p);
}
/*
* curpriority_cmp: Compare the priorities. Return:
* <0: p < curpriority
* 0: p == curpriority
* >0: p > curpriority
*/
static int
curpriority_cmp(struct proc *p)
{
priority_type prio = prioritize(p);
return prio - newcurpriority;
}
/*
* maybe_resched: Decide if you need to reschedule or not,
* taking the priorities and schedulers into account.
*
* This function needs to be call AFTER chk->p_priority has
* been updated.
*/
static void
maybe_resched(struct proc *chk)
{
if (curproc == 0)
need_resched();
else if (chk == curproc) {
/*
* If chk is curproc, we may need to preempt if
* we're making our priority less favorable.
*/
if (curpriority_cmp(chk) > 0) {
chk->p_stats->p_ru.ru_nvcsw++; /* <<< Adding */
need_resched();
}
}
/*
* If chk is not the curproc, we want to preempt if chk has
* a more favorable priority than curproc.
*
* We shouldn't preempt the current process because of the
* priority of a sleeping or stopped process.
*
*/
else if ((chk->p_flag & P_INMEM) &&
chk->p_stat == SRUN &&
curpriority_cmp(chk) < 0) {
need_resched();
}
}
--
Peter Dufault (dufault@hda.com) Realtime development, Machine control,
HD Associates, Inc. Safety critical systems, Agency approval
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