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.
Acked-by: Willem de Bruijn <willemb@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
Changes since V1:
- Add a comment to explain no overlapping when using memcpy
---
drivers/vhost/net.c | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 777eb6193985..a33a32a1e488 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -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);
@@ -715,12 +715,8 @@ 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);
--
2.34.1
