[SRU][B:linux-azure-4.15][PATCH 12/40] tuntap: XDP_TX can use native XDP

[William Breathitt Gray]

From: Jason Wang <jasowang at redhat.com>

BugLink: https://bugs.launchpad.net/bugs/1877654

Now we have ndo_xdp_xmit, switch to use it instead of the slow generic
XDP TX routine. XDP_TX on TAP gets ~20% improvements from ~1.5Mpps to
~1.8Mpps on 2.60GHz Core(TM) i7-5600U.

Signed-off-by: Jason Wang <jasowang at redhat.com>
Acked-by: Michael S. Tsirkin <mst at redhat.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(backported from commit 59655a5b6c837e392e873629591069c898585592)
[ vilhelmgray: context adjustments ]
[ vilhelmgray: use local_bh_enable() instead of preempt_enable() ]
Signed-off-by: William Breathitt Gray <william.gray at canonical.com>
---
 drivers/net/tun.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 6d827c0ef8cc..1d7f953d83e4 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1572,7 +1572,6 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	unsigned int delta = 0;
 	char *buf;
 	size_t copied;
-	bool xdp_xmit = false;
 	int err, pad = TUN_RX_PAD;
 
 	rcu_read_lock();
@@ -1630,8 +1629,14 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 			local_bh_enable();
 			return NULL;
 		case XDP_TX:
-			xdp_xmit = true;
-			/* fall through */
+			get_page(alloc_frag->page);
+			alloc_frag->offset += buflen;
+			if (tun_xdp_xmit(tun->dev, &xdp))
+				goto err_redirect;
+			tun_xdp_flush(tun->dev);
+			rcu_read_unlock();
+			local_bh_enable();
+			return NULL;
 		case XDP_PASS:
 			delta = orig_data - xdp.data;
 			break;
@@ -1659,14 +1664,6 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	get_page(alloc_frag->page);
 	alloc_frag->offset += buflen;
 
-	if (xdp_xmit) {
-		skb->dev = tun->dev;
-		generic_xdp_tx(skb, xdp_prog);
-		rcu_read_unlock();
-		local_bh_enable();
-		return NULL;
-	}
-
 	rcu_read_unlock();
 	local_bh_enable();
 
-- 
2.25.1