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| author | Rusty Russell <rusty@rustcorp.com.au> | 2012-01-12 09:14:43 +0400 |
|---|---|---|
| committer | Rusty Russell <rusty@rustcorp.com.au> | 2012-01-12 09:14:43 +0400 |
| commit | 3b720b8c865098c49c1570b6b5c7832bcfa6e6c2 (patch) | |
| tree | 7580908e53fb78ddc20945075d7f25408a6325fb /drivers/virtio | |
| parent | 41f0377f73039ca6fe97a469d1941a89cd9757f1 (diff) | |
| download | linux-3b720b8c865098c49c1570b6b5c7832bcfa6e6c2.tar.xz | |
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.c | 10 |
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); |