netdev - [bpf-next PATCH 1/3] xdp: unlikely instrumentation for xdp map redirect

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Date:   Fri, 31 Aug 2018 17:26:07 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     netdev@...r.kernel.org
Cc:     Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>
Subject: [bpf-next PATCH 1/3] xdp: unlikely instrumentation for xdp map
 redirect

Notice the compiler generated ASM code layout was suboptimal.  It
assumed map enqueue errors as the likely case, which is shouldn't.
It assumed that xdp_do_flush_map() was a likely case, due to maps
changing between packets, which should be very unlikely.

Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 net/core/filter.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index c25eb36f1320..520f5e9e0b73 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3182,7 +3182,7 @@ static int __bpf_tx_xdp_map(struct net_device *dev_rx, void *fwd,
 		struct bpf_dtab_netdev *dst = fwd;
 
 		err = dev_map_enqueue(dst, xdp, dev_rx);
-		if (err)
+		if (unlikely(err))
 			return err;
 		__dev_map_insert_ctx(map, index);
 		break;
@@ -3191,7 +3191,7 @@ static int __bpf_tx_xdp_map(struct net_device *dev_rx, void *fwd,
 		struct bpf_cpu_map_entry *rcpu = fwd;
 
 		err = cpu_map_enqueue(rcpu, xdp, dev_rx);
-		if (err)
+		if (unlikely(err))
 			return err;
 		__cpu_map_insert_ctx(map, index);
 		break;
@@ -3279,7 +3279,7 @@ static int xdp_do_redirect_map(struct net_device *dev, struct xdp_buff *xdp,
 		err = -EINVAL;
 		goto err;
 	}
-	if (ri->map_to_flush && ri->map_to_flush != map)
+	if (ri->map_to_flush && unlikely(ri->map_to_flush != map))
 		xdp_do_flush_map();
 
 	err = __bpf_tx_xdp_map(dev, fwd, map, xdp, index);