Author: davidxu
Date: Mon Jan 16 04:39:10 2012
New Revision: 230194
URL: http://svn.freebsd.org/changeset/base/230194
Log:
Eliminate branch and insert an explicit reader memory barrier to ensure
that waiter bit is set before reading semaphore count.
Modified:
head/sys/kern/kern_umtx.c
Modified: head/sys/kern/kern_umtx.c
==============================================================================
--- head/sys/kern/kern_umtx.c Mon Jan 16 04:09:45 2012 (r230193)
+++ head/sys/kern/kern_umtx.c Mon Jan 16 04:39:10 2012 (r230194)
@@ -2804,9 +2804,8 @@ do_sem_wait(struct thread *td, struct _u
umtxq_insert(uq);
umtxq_unlock(&uq->uq_key);
- if (fuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters)) == 0)
- casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1);
-
+ casuword32(__DEVOLATILE(uint32_t *, &sem->_has_waiters), 0, 1);
+ rmb();
count = fuword32(__DEVOLATILE(uint32_t *, &sem->_count));
if (count != 0) {
umtxq_lock(&uq->uq_key);
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