Device use descriptors table in order, so there's no need to read index from available ring. This eliminate the cache contention on avail ring completely. Virito-user + vhost_kernel + XDP_DROP gives about ~10% improvement on TX from 4.8Mpps to 5.3Mpps on Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz. Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx> --- drivers/vhost/vhost.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c index 3a5f81a66d34..c8be151bc897 100644 --- a/drivers/vhost/vhost.c +++ b/drivers/vhost/vhost.c @@ -2002,6 +2002,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq, __virtio16 avail_idx; __virtio16 ring_head; int ret, access; + bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER); /* Check it isn't doing very strange things with descriptor numbers. */ last_avail_idx = vq->last_avail_idx; @@ -2034,15 +2035,19 @@ 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(vhost_get_avail(vq, ring_head, - &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]); - return -EFAULT; + if (!in_order) { + if (unlikely(vhost_get_avail(vq, ring_head, + &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]); + return -EFAULT; + } + head = vhost16_to_cpu(vq, ring_head); + } else { + head = last_avail_idx & (vq->num - 1); } - head = vhost16_to_cpu(vq, ring_head); /* If their number is silly, that's an error. */ if (unlikely(head >= vq->num)) { -- 2.17.1 _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization