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hyperv/vmbus: Avoid unnecessary mb()

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MFC after:	1 week
Sponsored by:	Microsoft
Differential Revision:	https://reviews.freebsd.org/D7333
This commit is contained in:
Sepherosa Ziehau 2016-07-28 06:30:29 +00:00
parent 92ee0c01d4
commit 0bc135dffc
1 changed files with 3 additions and 17 deletions
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20
sys/dev/hyperv/vmbus/vmbus_br.c
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@ -209,9 +209,7 @@ vmbus_txbr_need_signal(const struct vmbus_txbr *tbr, uint32_t old_windex)
if (tbr->txbr_imask)
return (FALSE);
/* XXX only compiler fence is needed */
/* Read memory barrier */
rmb();
__compiler_membar();
/*
* This is the only case we need to signal when the
@ -307,16 +305,11 @@ vmbus_txbr_write(struct vmbus_txbr *tbr, const struct iovec iov[], int iovlen,
windex = vmbus_txbr_copyto(tbr, windex, &save_windex,
sizeof(save_windex));
/*
* XXX only compiler fence is needed.
* Full memory barrier before upding the write index.
*/
mb();
/*
* Update the write index _after_ the channel packet
* is copied.
*/
__compiler_membar();
tbr->txbr_windex = windex;
mtx_unlock_spin(&tbr->txbr_lock);
@ -395,17 +388,10 @@ vmbus_rxbr_read(struct vmbus_rxbr *rbr, void *data, int dlen, uint32_t skip)
*/
rindex = VMBUS_BR_IDXINC(rindex, sizeof(uint64_t), br_dsize);
/*
* XXX only compiler fence is needed.
* Make sure all reads are done before we update the read index since
* the writer may start writing to the read area once the read index
* is updated.
*/
wmb();
/*
* Update the read index _after_ the channel packet is fetched.
*/
__compiler_membar();
rbr->rxbr_rindex = rindex;
mtx_unlock_spin(&rbr->rxbr_lock);