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: Robert Shearman <rshearma@brocade.com> Signed-off-by: Roopa Prabhu <roopa@cumulusnetworks.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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@ -22,6 +22,11 @@
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#include <net/nexthop.h>
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#include "internal.h"
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/* Maximum number of labels to look ahead at when selecting a path of
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* a multipath route
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*/
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#define MAX_MP_SELECT_LABELS 4
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static int zero = 0;
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static int label_limit = (1 << 20) - 1;
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@ -77,10 +82,78 @@ bool mpls_pkt_too_big(const struct sk_buff *skb, unsigned int mtu)
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}
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EXPORT_SYMBOL_GPL(mpls_pkt_too_big);
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static struct mpls_nh *mpls_select_multipath(struct mpls_route *rt)
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static struct mpls_nh *mpls_select_multipath(struct mpls_route *rt,
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struct sk_buff *skb, bool bos)
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{
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/* assume single nexthop for now */
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return &rt->rt_nh[0];
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struct mpls_entry_decoded dec;
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struct mpls_shim_hdr *hdr;
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bool eli_seen = false;
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int label_index;
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int nh_index = 0;
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u32 hash = 0;
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/* No need to look further into packet if there's only
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* one path
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*/
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if (rt->rt_nhn == 1)
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goto out;
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for (label_index = 0; label_index < MAX_MP_SELECT_LABELS && !bos;
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label_index++) {
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if (!pskb_may_pull(skb, sizeof(*hdr) * label_index))
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break;
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/* Read and decode the current label */
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hdr = mpls_hdr(skb) + label_index;
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dec = mpls_entry_decode(hdr);
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/* RFC6790 - reserved labels MUST NOT be used as keys
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* for the load-balancing function
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*/
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if (likely(dec.label >= MPLS_LABEL_FIRST_UNRESERVED)) {
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hash = jhash_1word(dec.label, hash);
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/* The entropy label follows the entropy label
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* indicator, so this means that the entropy
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* label was just added to the hash - no need to
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* go any deeper either in the label stack or in the
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* payload
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*/
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if (eli_seen)
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break;
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} else if (dec.label == MPLS_LABEL_ENTROPY) {
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eli_seen = true;
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}
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bos = dec.bos;
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if (bos && pskb_may_pull(skb, sizeof(*hdr) * label_index +
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sizeof(struct iphdr))) {
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const struct iphdr *v4hdr;
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v4hdr = (const struct iphdr *)(mpls_hdr(skb) +
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label_index);
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if (v4hdr->version == 4) {
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hash = jhash_3words(ntohl(v4hdr->saddr),
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ntohl(v4hdr->daddr),
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v4hdr->protocol, hash);
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} else if (v4hdr->version == 6 &&
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pskb_may_pull(skb, sizeof(*hdr) * label_index +
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sizeof(struct ipv6hdr))) {
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const struct ipv6hdr *v6hdr;
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v6hdr = (const struct ipv6hdr *)(mpls_hdr(skb) +
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label_index);
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hash = __ipv6_addr_jhash(&v6hdr->saddr, hash);
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hash = __ipv6_addr_jhash(&v6hdr->daddr, hash);
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hash = jhash_1word(v6hdr->nexthdr, hash);
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}
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}
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}
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nh_index = hash % rt->rt_nhn;
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out:
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return &rt->rt_nh[nh_index];
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}
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static bool mpls_egress(struct mpls_route *rt, struct sk_buff *skb,
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@ -175,7 +248,7 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
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if (!rt)
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goto drop;
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nh = mpls_select_multipath(rt);
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nh = mpls_select_multipath(rt, skb, dec.bos);
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if (!nh)
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goto drop;
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@ -541,6 +614,12 @@ static int mpls_nh_build_multi(struct mpls_route_config *cfg,
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if (!rtnh_ok(rtnh, remaining))
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goto errout;
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/* neither weighted multipath nor any flags
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* are supported
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*/
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if (rtnh->rtnh_hops || rtnh->rtnh_flags)
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goto errout;
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attrlen = rtnh_attrlen(rtnh);
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if (attrlen > 0) {
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struct nlattr *attrs = rtnh_attrs(rtnh);
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