netdev - [RFC PATCH net-next 08/12] tuntap: tweak on the path of non-xdp case in tun_build

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Date:   Mon, 21 May 2018 17:04:29 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     mst@...hat.com, jasowang@...hat.com
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH net-next 08/12] tuntap: tweak on the path of non-xdp case in tun_build_skb()

If we're sure not to go native XDP, there's no need for several things
like touching preemption counter and rcu stuffs.

Signed-off-by: Jason Wang <jasowang@...hat.com>
---
 drivers/net/tun.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index f6e0f96..ed04291 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1645,10 +1645,12 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	 * of xdp_prog above, this should be rare and for simplicity
 	 * we do XDP on skb in case the headroom is not enough.
 	 */
-	if (hdr->gso_type || !xdp_prog)
+	if (hdr->gso_type || !xdp_prog) {
 		*skb_xdp = 1;
-	else
-		*skb_xdp = 0;
+		goto build;
+	}
+
+	*skb_xdp = 0;
 
 	preempt_disable();
 	rcu_read_lock();
@@ -1695,6 +1697,7 @@ static struct sk_buff *tun_build_skb(struct tun_struct *tun,
 	rcu_read_unlock();
 	preempt_enable();
 
+build:
 	skb = build_skb(buf, buflen);
 	if (!skb) {
 		skb = ERR_PTR(-ENOMEM);
-- 
2.7.4