I don't understand the resetpriority() function in the file
kern_synch.c in -current. I'm wondering if someone can help
me? What I don't understand is the logic for the call(s) to
maybe_resched() in resetpriority(). resetpriority() adjusts
kg->kg_user_pri, but doesn't touch td->td_priority. Therefore
the call(s) to maybe_resched() seems to be a no-op?
Now, if the callers of resetpriority() are fiddling with
td->td_priority before calling resetpriority(), then I could
maybe understand this. But, in every case I can see, the caller
of resetpriority() either does not change td->td_priority at all,
or it adjusts if _after_ the call to resetpriority(). Therefore,
it seems to me that maybe the call to maybe_resched not only is
a no-op, but perhaps the call should be made later, where needed,
by the callers to resetpriority()?
Thanks for any help.
>From kern_synch.c:
void
resetpriority(kg)
register struct ksegrp *kg;
{
register unsigned int newpriority;
struct thread *td;
mtx_lock_spin(&sched_lock);
if (kg->kg_pri_class == PRI_TIMESHARE) {
newpriority = PUSER + kg->kg_estcpu / INVERSE_ESTCPU_WEIGHT +
NICE_WEIGHT * (kg->kg_nice - PRIO_MIN);
newpriority = min(max(newpriority, PRI_MIN_TIMESHARE),
PRI_MAX_TIMESHARE);
kg->kg_user_pri = newpriority;
}
FOREACH_THREAD_IN_GROUP(kg, td) { <------ I don't understand
maybe_resched(td); <------ these
}
mtx_unlock_spin(&sched_lock);
}
and earlier:
void
maybe_resched(struct thread *td)
{
mtx_assert(&sched_lock, MA_OWNED);
if (td->td_priority < curthread->td_priority)
curthread->td_kse->ke_flags |= KEF_NEEDRESCHED;
}
--
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