netdev - [bpf-next V2 PATCH 3/3] xdp: split code for map vs non-map redirect

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Message-ID: <153596130766.4754.3649127914304146062.stgit@firesoul>
Date:   Mon, 03 Sep 2018 09:55:07 +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 V2 PATCH 3/3] xdp: split code for map vs non-map redirect

The compiler does an efficient job of inlining static C functions.
Perf top clearly shows that almost everything gets inlined into the
function call xdp_do_redirect.

The function xdp_do_redirect end-up containing and interleaving the
map and non-map redirect code.  This is sub-optimal, as it would be
strange for an XDP program to use both types of redirect in the same
program. The two use-cases are separate, and interleaving the code
just cause more instruction-cache pressure.

I would like to stress (again) that the non-map variant bpf_redirect
is very slow compared to the bpf_redirect_map variant, approx half the
speed.  Measured with driver i40e the difference is:

- map     redirect: 13,250,350 pps
- non-map redirect:  7,491,425 pps

For this reason, the function name of the non-map variant of redirect
have been called xdp_do_redirect_slow.  This hopefully gives a hint
when using perf, that this is not the optimal XDP redirect operating mode.

Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
---
 net/core/filter.c |   52 ++++++++++++++++++++++++++++++----------------------
 1 file changed, 30 insertions(+), 22 deletions(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index ec1b4eb0d3d4..7738d1d70154 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3170,6 +3170,32 @@ static int __bpf_tx_xdp(struct net_device *dev,
 	return 0;
 }
 
+static noinline int
+xdp_do_redirect_slow(struct net_device *dev, struct xdp_buff *xdp,
+		     struct bpf_prog *xdp_prog, struct bpf_redirect_info *ri)
+{
+	struct net_device *fwd;
+	u32 index = ri->ifindex;
+	int err;
+
+	fwd = dev_get_by_index_rcu(dev_net(dev), index);
+	ri->ifindex = 0;
+	if (unlikely(!fwd)) {
+		err = -EINVAL;
+		goto err;
+	}
+
+	err = __bpf_tx_xdp(fwd, NULL, xdp, 0);
+	if (unlikely(err))
+		goto err;
+
+	_trace_xdp_redirect(dev, xdp_prog, index);
+	return 0;
+err:
+	_trace_xdp_redirect_err(dev, xdp_prog, index, err);
+	return err;
+}
+
 static int __bpf_tx_xdp_map(struct net_device *dev_rx, void *fwd,
 			    struct bpf_map *map,
 			    struct xdp_buff *xdp,
@@ -3264,9 +3290,9 @@ void bpf_clear_redirect_map(struct bpf_map *map)
 }
 
 static int xdp_do_redirect_map(struct net_device *dev, struct xdp_buff *xdp,
-			       struct bpf_prog *xdp_prog, struct bpf_map *map)
+			       struct bpf_prog *xdp_prog, struct bpf_map *map,
+			       struct bpf_redirect_info *ri)
 {
-	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
 	u32 index = ri->ifindex;
 	void *fwd = NULL;
 	int err;
@@ -3299,29 +3325,11 @@ int xdp_do_redirect(struct net_device *dev, struct xdp_buff *xdp,
 {
 	struct bpf_redirect_info *ri = this_cpu_ptr(&bpf_redirect_info);
 	struct bpf_map *map = READ_ONCE(ri->map);
-	struct net_device *fwd;
-	u32 index = ri->ifindex;
-	int err;
 
 	if (likely(map))
-		return xdp_do_redirect_map(dev, xdp, xdp_prog, map);
+		return xdp_do_redirect_map(dev, xdp, xdp_prog, map, ri);
 
-	fwd = dev_get_by_index_rcu(dev_net(dev), index);
-	ri->ifindex = 0;
-	if (unlikely(!fwd)) {
-		err = -EINVAL;
-		goto err;
-	}
-
-	err = __bpf_tx_xdp(fwd, NULL, xdp, 0);
-	if (unlikely(err))
-		goto err;
-
-	_trace_xdp_redirect(dev, xdp_prog, index);
-	return 0;
-err:
-	_trace_xdp_redirect_err(dev, xdp_prog, index, err);
-	return err;
+	return xdp_do_redirect_slow(dev, xdp, xdp_prog, ri);
 }
 EXPORT_SYMBOL_GPL(xdp_do_redirect);