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authorRusty Russell <rusty@rustcorp.com.au>2012-01-12 15:44:43 +1030
committerRusty Russell <rusty@rustcorp.com.au>2012-01-12 15:44:43 +1030
commit3b720b8c865098c49c1570b6b5c7832bcfa6e6c2 (patch)
tree7580908e53fb78ddc20945075d7f25408a6325fb /drivers/virtio
parent41f0377f73039ca6fe97a469d1941a89cd9757f1 (diff)
virtio: avoid modulus operation.
Since we know vq->vring.num is a power of 2, modulus is lazy (it's asserted in vring_new_virtqueue()). Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Diffstat (limited to 'drivers/virtio')
-rw-r--r--drivers/virtio/virtio_ring.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index c56bbe799241..99dc9480f3fe 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -250,8 +250,8 @@ add_head:
vq->data[head] = data;
/* Put entry in available array (but don't update avail->idx until they
- * do sync). FIXME: avoid modulus here? */
- avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num;
+ * do sync). */
+ avail = ((vq->vring.avail->idx + vq->num_added++) & (vq->vring.num-1));
vq->vring.avail->ring[avail] = head;
pr_debug("Added buffer head %i to %p\n", head, vq);
@@ -384,6 +384,7 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
struct vring_virtqueue *vq = to_vvq(_vq);
void *ret;
unsigned int i;
+ u16 last_used;
START_USE(vq);
@@ -401,8 +402,9 @@ void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
/* Only get used array entries after they have been exposed by host. */
virtio_rmb(vq);
- i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
- *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;
+ last_used = (vq->last_used_idx & (vq->vring.num - 1));
+ i = vq->vring.used->ring[last_used].id;
+ *len = vq->vring.used->ring[last_used].len;
if (unlikely(i >= vq->vring.num)) {
BAD_RING(vq, "id %u out of range\n", i);