Commit 1c78efa8 authored by Robert Shearman's avatar Robert Shearman Committed by David S. Miller
Browse files

mpls: flow-based multipath selection 



Change the selection of a multipath route to use a flow-based
hash. This more suitable for traffic sensitive to reordering within a
flow (e.g. TCP, L2VPN) and whilst still allowing a good distribution
of traffic given enough flows.

Selection of the path for a multipath route is done using a hash of:
1. Label stack up to MAX_MP_SELECT_LABELS labels or up to and
   including entropy label, whichever is first.
2. 3-tuple of (L3 src, L3 dst, proto) from IPv4/IPv6 header in MPLS
   payload, if present.

Naturally, a 5-tuple hash using L4 information in addition would be
possible and be better in some scenarios, but there is a tradeoff
between looking deeper into the packet to achieve good distribution,
and packet forwarding performance, and I have erred on the side of the
latter as the default.

Signed-off-by: default avatarRobert Shearman <rshearma@brocade.com>
Signed-off-by: default avatarRoopa Prabhu <roopa@cumulusnetworks.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent f8efb73c

net/mpls/af_mpls.c

+83 −4
Original line number Diff line number Diff line
@@ -22,6 +22,11 @@ 
#include <net/nexthop.h>

#include "internal.h"



/* Maximum number of labels to look ahead at when selecting a path of

 * a multipath route

 */

#define MAX_MP_SELECT_LABELS 4



static int zero = 0;

static int label_limit = (1 << 20) - 1;
@@ -77,10 +82,78 @@ bool mpls_pkt_too_big(const struct sk_buff *skb, unsigned int mtu) 
}

EXPORT_SYMBOL_GPL(mpls_pkt_too_big);



static struct mpls_nh *mpls_select_multipath(struct mpls_route *rt)

static struct mpls_nh *mpls_select_multipath(struct mpls_route *rt,

					     struct sk_buff *skb, bool bos)

{

	/* assume single nexthop for now */

	return &rt->rt_nh[0];

	struct mpls_entry_decoded dec;

	struct mpls_shim_hdr *hdr;

	bool eli_seen = false;

	int label_index;

	int nh_index = 0;

	u32 hash = 0;



	/* No need to look further into packet if there's only

	 * one path

	 */

	if (rt->rt_nhn == 1)

		goto out;



	for (label_index = 0; label_index < MAX_MP_SELECT_LABELS && !bos;

	     label_index++) {

		if (!pskb_may_pull(skb, sizeof(*hdr) * label_index))

			break;



		/* Read and decode the current label */

		hdr = mpls_hdr(skb) + label_index;

		dec = mpls_entry_decode(hdr);



		/* RFC6790 - reserved labels MUST NOT be used as keys

		 * for the load-balancing function

		 */

		if (likely(dec.label >= MPLS_LABEL_FIRST_UNRESERVED)) {

			hash = jhash_1word(dec.label, hash);



			/* The entropy label follows the entropy label

			 * indicator, so this means that the entropy

			 * label was just added to the hash - no need to

			 * go any deeper either in the label stack or in the

			 * payload

			 */

			if (eli_seen)

				break;

		} else if (dec.label == MPLS_LABEL_ENTROPY) {

			eli_seen = true;

		}



		bos = dec.bos;

		if (bos && pskb_may_pull(skb, sizeof(*hdr) * label_index +

					 sizeof(struct iphdr))) {

			const struct iphdr *v4hdr;



			v4hdr = (const struct iphdr *)(mpls_hdr(skb) +

						       label_index);

			if (v4hdr->version == 4) {

				hash = jhash_3words(ntohl(v4hdr->saddr),

						    ntohl(v4hdr->daddr),

						    v4hdr->protocol, hash);

			} else if (v4hdr->version == 6 &&

				pskb_may_pull(skb, sizeof(*hdr) * label_index +

					      sizeof(struct ipv6hdr))) {

				const struct ipv6hdr *v6hdr;



				v6hdr = (const struct ipv6hdr *)(mpls_hdr(skb) +

								label_index);



				hash = __ipv6_addr_jhash(&v6hdr->saddr, hash);

				hash = __ipv6_addr_jhash(&v6hdr->daddr, hash);

				hash = jhash_1word(v6hdr->nexthdr, hash);

			}

		}

	}



	nh_index = hash % rt->rt_nhn;

out:

	return &rt->rt_nh[nh_index];

}



static bool mpls_egress(struct mpls_route *rt, struct sk_buff *skb,
@@ -175,7 +248,7 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev, 
	if (!rt)

		goto drop;



	nh = mpls_select_multipath(rt);

	nh = mpls_select_multipath(rt, skb, dec.bos);

	if (!nh)

		goto drop;
@@ -541,6 +614,12 @@ static int mpls_nh_build_multi(struct mpls_route_config *cfg, 
		if (!rtnh_ok(rtnh, remaining))

			goto errout;



		/* neither weighted multipath nor any flags

		 * are supported

		 */

		if (rtnh->rtnh_hops || rtnh->rtnh_flags)

			goto errout;



		attrlen = rtnh_attrlen(rtnh);

		if (attrlen > 0) {

			struct nlattr *attrs = rtnh_attrs(rtnh);

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