From: Jesper Dangaard Brouer <brouer@redhat.com>
Date: Thu, 31 May 2018 11:00:18 +0200
Subject: bpf/xdp: non-map redirect can avoid calling ndo_xdp_flush
Patch-mainline: v4.18-rc1
Git-commit: 1e67575a5840908e33502b210a22509fe5d6ca53
References: bsc#1109837

This is the first real user of the XDP_XMIT_FLUSH flag.

As pointed out many times, XDP_REDIRECT without using BPF maps is
significant slower than the map variant.  This is primary due to the
lack of bulking, as the ndo_xdp_flush operation is required after each
frame (to avoid frames hanging on the egress device).

It is still possible to optimize this case.  Instead of invoking two
NDO indirect calls, which are very expensive with CONFIG_RETPOLINE,
instead instruct ndo_xdp_xmit to flush via XDP_XMIT_FLUSH flag.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/core/filter.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3036,10 +3036,9 @@ static int __bpf_tx_xdp(struct net_devic
 	if (unlikely(!xdpf))
 		return -EOVERFLOW;
 
-	sent = dev->netdev_ops->ndo_xdp_xmit(dev, 1, &xdpf, 0);
+	sent = dev->netdev_ops->ndo_xdp_xmit(dev, 1, &xdpf, XDP_XMIT_FLUSH);
 	if (sent <= 0)
 		return sent;
-	dev->netdev_ops->ndo_xdp_flush(dev);
 	return 0;
 }