Re: [PATCH v2] vhost: replace % with & on data path
From: Christian Borntraeger <hidden>
Date: 2015-11-30 09:21:58
Also in:
kvm, lkml, netdev
On 11/30/2015 10:15 AM, Michael S. Tsirkin wrote:
We know vring num is a power of 2, so use & to mask the high bits.
Makes a lot of sense and virtio_ring.c seems to use the same logic. Acked-by: Christian Borntraeger <redacted>
quoted hunk ↗ jump to hunk
Signed-off-by: Michael S. Tsirkin <mst@redhat.com> --- Changes from v1: drop an unrelated chunk drivers/vhost/vhost.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 080422f..ad2146a 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c@@ -1369,7 +1369,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, /* 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 +1489,7 @@ 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 +1531,7 @@ 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);