vhost-net only uses memory barriers to control SMP effects
(communication with userspace potentially running on a different CPU),
so it should use SMP barriers and not mandatory barriers for memory
access ordering, as suggested by Documentation/memory-barriers.txt
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
drivers/vhost/vhost.c | 10 +++++-----
1 files changed, 5 insertions(+), 5 deletions(-)
The above applies on top of net-next-2.6. Does not seem to give any
measureable performance gain, but seems to generate less code
and I think it's better to use correct APIs.
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index c8c25db..6eb1525 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -685,7 +685,7 @@ int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
int i, r;
/* Make sure data written is seen before log. */
- wmb();
+ smp_wmb();
for (i = 0; i < log_num; ++i) {
u64 l = min(log[i].len, len);
r = log_write(vq->log_base, log[i].addr, l);
@@ -884,7 +884,7 @@ unsigned vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
return vq->num;
/* Only get avail ring entries after they have been exposed by guest. */
- rmb();
+ smp_rmb();
/* Grab the next descriptor number they're advertising, and increment
* the index we've seen. */
@@ -996,14 +996,14 @@ int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
return -EFAULT;
}
/* Make sure buffer is written before we update index. */
- wmb();
+ smp_wmb();
if (put_user(vq->last_used_idx + 1, &vq->used->idx)) {
vq_err(vq, "Failed to increment used idx");
return -EFAULT;
}
if (unlikely(vq->log_used)) {
/* Make sure data is seen before log. */
- wmb();
+ smp_wmb();
log_write(vq->log_base, vq->log_addr + sizeof *vq->used->ring *
(vq->last_used_idx % vq->num),
sizeof *vq->used->ring);
@@ -1060,7 +1060,7 @@ bool vhost_enable_notify(struct vhost_virtqueue *vq)
}
/* They could have slipped one in as we were doing that: make
* sure it's written, then check again. */
- mb();
+ smp_mb();
r = get_user(avail_idx, &vq->avail->idx);
if (r) {
vq_err(vq, "Failed to check avail idx at %p: %d\n",
--
1.6.6.144.g5c3af
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