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Prevent preemption in slot_fill.

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Implement preemption between threads in the same ksegp in out of slot
situations to prevent priority inversion.

Tested   by: pho
Reviewed by: jhb, julian
Approved by: sam (mentor)
MFC: ASAP
This commit is contained in:
Stephan Uphoff 2004-10-12 16:30:20 +00:00
parent b9a80acadb
commit 84f9d4b137
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=136438
1 changed files with 110 additions and 1 deletions
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111
sys/kern/kern_switch.c
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@ -214,7 +214,7 @@ slot_fill(struct ksegrp *kg)
*/
if (td) {
kg->kg_last_assigned = td;
sched_add(td, SRQ_BORING);
sched_add(td, SRQ_YIELDING);
CTR2(KTR_RUNQ, "slot_fill: td%p -> kg%p", td, kg);
} else {
/* no threads to use up the slots. quit now */
@ -315,6 +315,113 @@ adjustrunqueue( struct thread *td, int newpri)
td->td_priority = newpri;
setrunqueue(td, SRQ_BORING);
}
/*
* This function is called when a thread is about to be put on a
* ksegrp run queue because it has been made runnable or its
* priority has been adjusted and the ksegrp does not have a
* free kse slot. It determines if a thread from the same ksegrp
* should be preempted. If so, it tries to switch threads
* if the thread is on the same cpu or notifies another cpu that
* it should switch threads.
*/
static void
maybe_preempt_in_ksegrp(struct thread *td)
{
#if defined(SMP)
int worst_pri;
struct ksegrp *kg;
cpumask_t cpumask,dontuse;
struct pcpu *pc;
struct pcpu *best_pcpu;
struct thread *running_thread;
struct thread *cputhread;
#ifndef FULL_PREEMPTION
int pri;
pri = td->td_priority;
if (!(pri >= PRI_MIN_ITHD && pri <= PRI_MAX_ITHD))
return;
#endif
mtx_assert(&sched_lock, MA_OWNED);
running_thread = curthread;
#if !defined(KSEG_PEEMPT_BEST_CPU)
if (running_thread->td_ksegrp != td->td_ksegrp) {
#endif
kg = td->td_ksegrp;
/* if someone is ahead of this thread, wait our turn */
if (td != TAILQ_FIRST(&kg->kg_runq))
return;
worst_pri = td->td_priority;
best_pcpu = NULL;
dontuse = stopped_cpus | idle_cpus_mask;
/*
* Find a cpu with the worst priority that runs at thread from
* the same ksegrp - if multiple exist give first the last run
* cpu and then the current cpu priority
*/
SLIST_FOREACH(pc, &cpuhead, pc_allcpu) {
cpumask = pc->pc_cpumask;
cputhread = pc->pc_curthread;
if ((cpumask & dontuse) ||
cputhread->td_ksegrp != kg)
continue;
if (cputhread->td_priority > worst_pri) {
worst_pri = cputhread->td_priority;
best_pcpu = pc;
continue;
}
if (cputhread->td_priority == worst_pri &&
best_pcpu != NULL &&
(td->td_lastcpu == pc->pc_cpuid ||
(PCPU_GET(cpumask) == cpumask &&
td->td_lastcpu != best_pcpu->pc_cpuid)))
best_pcpu = pc;
}
/* Check if we need to preempt someone */
if (best_pcpu == NULL)
return;
if (PCPU_GET(cpuid) != best_pcpu->pc_cpuid) {
best_pcpu->pc_curthread->td_flags |= TDF_NEEDRESCHED;
ipi_selected(best_pcpu->pc_cpumask, IPI_AST);
return;
}
#if !defined(KSEG_PEEMPT_BEST_CPU)
}
#endif
#else
KASSERT(running_thread->td_ksegrp == td->td_ksegrp,
("maybe_preempt_in_ksegrp: No chance to run thread"));
#endif
if (td->td_priority > running_thread->td_priority)
return;
#ifdef PREEMPTION
if (running_thread->td_critnest > 1)
running_thread->td_pflags |= TDP_OWEPREEMPT;
else
mi_switch(SW_INVOL, NULL);
#else
running_thread->td_flags |= TDF_NEEDRESCHED;
#endif
return;
}
int limitcount;
void
setrunqueue(struct thread *td, int flags)
@ -421,6 +528,8 @@ setrunqueue(struct thread *td, int flags)
} else {
CTR3(KTR_RUNQ, "setrunqueue: held: td%p kg%p pid%d",
td, td->td_ksegrp, td->td_proc->p_pid);
if ((flags & SRQ_YIELDING) == 0)
maybe_preempt_in_ksegrp(td);
}
}