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sx: perform a minor cleanup of the unlock slowpath

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No functional changes.
This commit is contained in:
mjg 2017-11-17 02:27:04 +00:00
parent 45ffcf24ba
commit 2cadb364c5
1 changed files with 9 additions and 7 deletions
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16
sys/kern/kern_sx.c
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@ -772,7 +772,7 @@ _sx_xlock_hard(struct sx *sx, uintptr_t x, uintptr_t tid, int opts,
void
_sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
{
uintptr_t x;
uintptr_t x, setx;
int queue, wakeup_swapper;
if (SCHEDULER_STOPPED())
@ -801,7 +801,7 @@ _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
CTR2(KTR_LOCK, "%s: %p contested", __func__, sx);
sleepq_lock(&sx->lock_object);
x = SX_LOCK_UNLOCKED;
x = SX_READ_VALUE(sx);
/*
* The wake up algorithm here is quite simple and probably not
@ -812,19 +812,21 @@ _sx_xunlock_hard(struct sx *sx, uintptr_t tid, const char *file, int line)
* starvation for the threads sleeping on the exclusive queue by giving
* them precedence and cleaning up the shared waiters bit anyway.
*/
if ((sx->sx_lock & SX_LOCK_SHARED_WAITERS) != 0 &&
setx = SX_LOCK_UNLOCKED;
queue = SQ_EXCLUSIVE_QUEUE;
if ((x & SX_LOCK_SHARED_WAITERS) != 0 &&
sleepq_sleepcnt(&sx->lock_object, SQ_SHARED_QUEUE) != 0) {
queue = SQ_SHARED_QUEUE;
x |= (sx->sx_lock & SX_LOCK_EXCLUSIVE_WAITERS);
} else
queue = SQ_EXCLUSIVE_QUEUE;
setx |= (x & SX_LOCK_EXCLUSIVE_WAITERS);
}
atomic_store_rel_ptr(&sx->sx_lock, setx);
/* Wake up all the waiters for the specific queue. */
if (LOCK_LOG_TEST(&sx->lock_object, 0))
CTR3(KTR_LOCK, "%s: %p waking up all threads on %s queue",
__func__, sx, queue == SQ_SHARED_QUEUE ? "shared" :
"exclusive");
atomic_store_rel_ptr(&sx->sx_lock, x);
wakeup_swapper = sleepq_broadcast(&sx->lock_object, SLEEPQ_SX, 0,
queue);
sleepq_release(&sx->lock_object);