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

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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: Jason Wang <jasowang@redhat.com>
Link: https://patch.msgid.link/20250701010352.74515-2-jasowang@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jason Wang 2025-07-01 09:03:52 +08:00 committed by Jakub Kicinski
parent 4d313f2bd2
commit 97b2409f28
1 changed files with 6 additions and 10 deletions
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16
drivers/vhost/net.c
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@ -690,13 +690,13 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
if (unlikely(!buf)) if (unlikely(!buf))
return -ENOMEM; return -ENOMEM;
copied = copy_from_iter(buf, sock_hlen, from); copied = copy_from_iter(buf + pad - sock_hlen, len, from);
if (copied != sock_hlen) { if (copied != len) {
ret = -EFAULT; ret = -EFAULT;
goto err; goto err;
} }
gso = buf; gso = buf + pad - sock_hlen;
if (!sock_hlen) if (!sock_hlen)
memset(buf, 0, pad); memset(buf, 0, pad);
@ -715,15 +715,11 @@ static int vhost_net_build_xdp(struct vhost_net_virtqueue *nvq,
} }
} }
len -= sock_hlen; /* pad contains sock_hlen */
copied = copy_from_iter(buf + pad, len, from); memcpy(buf, buf + pad - sock_hlen, sock_hlen);
if (copied != len) {
ret = -EFAULT;
goto err;
}
xdp_init_buff(xdp, buflen, NULL); 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; ++nvq->batched_xdp;