Commit 97b2409f authored by Jason Wang's avatar Jason Wang Committed by Jakub Kicinski
Browse files

vhost-net: reduce one userspace copy when building XDP buff 



We used to do twice copy_from_iter() to copy virtio-net and packet
separately. This introduce overheads for userspace access hardening as
well as SMAP (for x86 it's stac/clac). So this patch tries to use one
copy_from_iter() to copy them once and move the virtio-net header
afterwards to reduce overheads.

Testpmd + vhost_net shows 10% improvement from 5.45Mpps to 6.0Mpps.

Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
Link: https://patch.msgid.link/20250701010352.74515-2-jasowang@redhat.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 4d313f2b

drivers/vhost/net.c

+6 −10
Original line number Diff line number Diff line
@@ -690,13 +690,13 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq, 
	if (unlikely(!buf))

		return -ENOMEM;



	copied = copy_from_iter(buf, sock_hlen, from);

	if (copied != sock_hlen) {

	copied = copy_from_iter(buf + pad - sock_hlen, len, from);

	if (copied != len) {

		ret = -EFAULT;

		goto err;

	}



	gso = buf;

	gso = buf + pad - sock_hlen;



	if (!sock_hlen)

		memset(buf, 0, pad);
@@ -715,15 +715,11 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq, 
		}

	}



	len -= sock_hlen;

	copied = copy_from_iter(buf + pad, len, from);

	if (copied != len) {

		ret = -EFAULT;

		goto err;

	}

	/* pad contains sock_hlen */

	memcpy(buf, buf + pad - sock_hlen, sock_hlen);



	xdp_init_buff(xdp, buflen, NULL);

	xdp_prepare_buff(xdp, buf, pad, len, true);

	xdp_prepare_buff(xdp, buf, pad, len - sock_hlen, true);



	++nvq->batched_xdp;