Messages in this thread Patch in this message | | | Date | Mon, 30 Nov 2015 10:34:07 +0200 | From | "Michael S. Tsirkin" <> | Subject | [PATCH] vhost: replace % with & on data path |
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We know vring num is a power of 2, so use & to mask the high bits.
Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- drivers/vhost/vhost.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 080422f..85f0f0a 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -1366,10 +1366,12 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, /* Only get avail ring entries after they have been exposed by guest. */ smp_rmb(); + } + /* Grab the next descriptor number they're advertising, and increment * the index we've seen. */ if (unlikely(__get_user(ring_head, - &vq->avail->ring[last_avail_idx % vq->num]))) { + &vq->avail->ring[last_avail_idx & (vq->num - 1)]))) { vq_err(vq, "Failed to read head: idx %d address %p\n", last_avail_idx, &vq->avail->ring[last_avail_idx % vq->num]); @@ -1489,7 +1491,7 @@ static int __vhost_add_used_n(struct vhost_virtqueue *vq, u16 old, new; int start; - start = vq->last_used_idx % vq->num; + start = vq->last_used_idx & (vq->num - 1); used = vq->used->ring + start; if (count == 1) { if (__put_user(heads[0].id, &used->id)) { @@ -1531,7 +1533,7 @@ int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads, { int start, n, r; - start = vq->last_used_idx % vq->num; + start = vq->last_used_idx & (vq->num - 1); n = vq->num - start; if (n < count) { r = __vhost_add_used_n(vq, heads, n); -- MST
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