[PATCH net-next 3/3] vhost: don't touch avail ring if in_order is negotiated
From: Jason Wang <jasowang@redhat.com>
Date: 2018-11-23 03:00:55
Also in:
kvm, lkml
Subsystem:
the rest, virtio host (vhost) · Maintainers:
Linus Torvalds, "Michael S. Tsirkin", Jason Wang
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@redhat.com> --- 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