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Use sleepq_signal(SLEEPQ_DROP) in cv_signal().

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Same as wakeup_one()/wakeup_any() commit before it reduces the lock
hold time and so contention.

MFC after:	1 week
This commit is contained in:
Alexander Motin 2021-07-09 20:52:40 -04:00
parent 588c7a06df
commit 63ca9ea4f3
1 changed files with 12 additions and 15 deletions
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27
sys/kern/kern_condvar.c
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@ -397,26 +397,23 @@ _cv_timedwait_sig_sbt(struct cv *cvp, struct lock_object *lock,
void
cv_signal(struct cv *cvp)
{
int wakeup_swapper;
if (cvp->cv_waiters == 0)
return;
wakeup_swapper = 0;
sleepq_lock(cvp);
if (cvp->cv_waiters > 0) {
if (cvp->cv_waiters == CV_WAITERS_BOUND &&
sleepq_lookup(cvp) == NULL) {
cvp->cv_waiters = 0;
} else {
if (cvp->cv_waiters < CV_WAITERS_BOUND)
cvp->cv_waiters--;
wakeup_swapper = sleepq_signal(cvp, SLEEPQ_CONDVAR, 0,
0);
}
if (cvp->cv_waiters == 0) {
sleepq_release(cvp);
return;
}
if (cvp->cv_waiters == CV_WAITERS_BOUND && sleepq_lookup(cvp) == NULL) {
cvp->cv_waiters = 0;
sleepq_release(cvp);
} else {
if (cvp->cv_waiters < CV_WAITERS_BOUND)
cvp->cv_waiters--;
if (sleepq_signal(cvp, SLEEPQ_CONDVAR | SLEEPQ_DROP, 0, 0))
kick_proc0();
}
sleepq_release(cvp);
if (wakeup_swapper)
kick_proc0();
}
/*