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Date: Tue, 28 Jul 2015 02:27:57 +0000
From: Richard Laing <Richard.Laing@...iedtelesis.co.nz>
To: "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC: "jmorris@...ei.org" <jmorris@...ei.org>
Subject: [RFC PATCH 1/1] net/ipv4: Enable flow-based ECMP
From: Richard Laing <richard.laing@...iedtelesis.co.nz>
Enable flow-based ECMP.
Currently if equal-cost multipath is enabled the kernel chooses between
equal cost paths for each matching packet, essentially packets are
round-robined between the routes. This means that packets from a single
flow can traverse different routes. If one of the routes experiences
congestion this can result in delayed or out of order packets arriving
at the destination.
This patch allows packets to be routed based on their
flow - packets in the same flow will always use the same route. This
prevents out of order packets. There are other issues with round-robin
based ECMP routing related to variable path MTU handling and debugging.
See RFC2991 for more details on the problems associated with packet
based ECMP routing.
This patch relies on the skb hash value to select between routes. The
selection uses a hash-threshold algorithm (see RFC2992).
Signed-off-by: Richard Laing <richard.laing@...iedtelesis.co.nz>
---
include/net/flow.h | 14 ++++++++++++++
include/net/ip_fib.h | 9 +++++++++
include/net/route.h | 4 ++++
net/ipv4/Kconfig | 9 +++++++++
net/ipv4/fib_semantics.c | 38 ++++++++++++++++++++++++++++++++++++++
net/ipv4/route.c | 14 +++++++++++++-
6 files changed, 87 insertions(+), 1 deletion(-)
diff --git a/include/net/flow.h b/include/net/flow.h
index 8109a15..d1d933d 100644
--- a/include/net/flow.h
+++ b/include/net/flow.h
@@ -79,6 +79,10 @@ struct flowi4 {
#define fl4_ipsec_spi uli.spi
#define fl4_mh_type uli.mht.type
#define fl4_gre_key uli.gre_key
+
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+ __u32 flowi4_hash;
+#endif
} __attribute__((__aligned__(BITS_PER_LONG/8)));
static inline void flowi4_init_output(struct flowi4 *fl4, int oif,
@@ -99,6 +103,9 @@ static inline void flowi4_init_output(struct flowi4
*fl4, int oif,
fl4->saddr = saddr;
fl4->fl4_dport = dport;
fl4->fl4_sport = sport;
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+ fl4->flowi4_hash = 0;
+#endif
}
/* Reset some input parameters after previous lookup */
@@ -182,6 +189,13 @@ static inline struct flowi *flowidn_to_flowi(struct
flowidn *fldn)
return container_of(fldn, struct flowi, u.dn);
}
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+static inline void flowi4_set_flow_hash(struct flowi4 *fl, __u32 hash)
+{
+ fl->flowi4_hash = hash;
+}
+#endif
+
typedef unsigned long flow_compare_t;
static inline size_t flow_key_size(u16 family)
diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 5fa643b..c841698 100644
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -117,6 +117,10 @@ struct fib_info {
#ifdef CONFIG_IP_ROUTE_MULTIPATH
int fib_power;
#endif
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+ /* Cache the number of live nexthops for flow based ECMP
calculation. */
+ int live_nexthops;
+#endif
struct rcu_head rcu;
struct fib_nh fib_nh[0];
#define fib_dev fib_nh[0].nh_dev
@@ -311,6 +315,11 @@ int fib_sync_down_addr(struct net *net, __be32 local);
int fib_sync_up(struct net_device *dev, unsigned int nh_flags);
void fib_select_multipath(struct fib_result *res);
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+void fib_select_multipath_for_flow(struct fib_result *res,
+ const struct flowi4 *fl4);
+#endif
+
/* Exported by fib_trie.c */
void fib_trie_init(void);
struct fib_table *fib_trie_table(u32 id, struct fib_table *alias);
diff --git a/include/net/route.h b/include/net/route.h
index fe22d03..fdbbe7f 100644
--- a/include/net/route.h
+++ b/include/net/route.h
@@ -252,6 +252,10 @@ static inline void ip_route_connect_init(struct
flowi4 *fl4, __be32 dst, __be32
flowi4_init_output(fl4, oif, sk->sk_mark, tos, RT_SCOPE_UNIVERSE,
protocol, flow_flags, dst, src, dport, sport);
+
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+ flowi4_set_flow_hash(fl4, sk->sk_hash);
+#endif
}
static inline struct rtable *ip_route_connect(struct flowi4 *fl4,
diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
index 6fb3c90..76714d0 100644
--- a/net/ipv4/Kconfig
+++ b/net/ipv4/Kconfig
@@ -90,6 +90,15 @@ config IP_ROUTE_MULTIPATH
equal "cost" and chooses one of them in a non-deterministic fashion
if a matching packet arrives.
+config IP_FLOW_BASED_MULTIPATH
+ bool "IP: flow based equal cost multipath"
+ depends on IP_ROUTE_MULTIPATH
+ help
+ Normally if equal cost multipath is enabled the router chooses
between
+ equal "cost" paths for each matching packet, essentially
packets are round-
+ robined between the routes. This option allows packets to be
routed based on
+ their flow - packets in the same flow will always use the
same route.
+
config IP_ROUTE_VERBOSE
bool "IP: verbose route monitoring"
depends on IP_ADVANCED_ROUTER
diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 3a06586..e4750e6 100644
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -981,6 +981,9 @@ link_it:
head = &fib_info_devhash[hash];
hlist_add_head(&nexthop_nh->nh_hash, head);
} endfor_nexthops(fi)
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+ fi->live_nexthops = fi->fib_nhs;
+#endif
spin_unlock_bh(&fib_info_lock);
return fi;
@@ -1196,6 +1199,9 @@ int fib_sync_down_dev(struct net_device *dev,
unsigned long event)
}
ret++;
}
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+ fi->live_nexthops = fi->fib_nhs - dead;
+#endif
}
return ret;
@@ -1331,6 +1337,9 @@ int fib_sync_up(struct net_device *dev, unsigned
int nh_flags)
if (alive > 0) {
fi->fib_flags &= ~nh_flags;
ret++;
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+ fi->live_nexthops = alive;
+#endif
}
}
@@ -1397,4 +1406,33 @@ void fib_select_multipath(struct fib_result *res)
res->nh_sel = 0;
spin_unlock_bh(&fib_multipath_lock);
}
+
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+void fib_select_multipath_for_flow(struct fib_result *res,
+ const struct flowi4 *fl4)
+{
+ struct fib_info *fi = res->fi;
+ int multipath_entry;
+ int region_size;
+
+ if (fl4->flowi4_hash) {
+ /* Hash-threshold algorithm, see RFC2992. */
+ region_size = U32_MAX / fi->live_nexthops;
+ multipath_entry = fl4->flowi4_hash / region_size;
+
+ spin_lock_bh(&fib_multipath_lock);
+ for_nexthops(fi) {
+ if (!(nh->nh_flags & RTNH_F_DEAD)) {
+ res->nh_sel = nhsel;
+ if (multipath_entry == 0)
+ break;
+ multipath_entry--;
+ }
+ } endfor_nexthops(fi);
+ spin_unlock_bh(&fib_multipath_lock);
+ } else {
+ fib_select_multipath(res);
+ }
+}
+#endif
#endif
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index e681b85..4629c04 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1638,9 +1638,17 @@ static int ip_mkroute_input(struct sk_buff *skb,
__be32 daddr, __be32 saddr, u32 tos)
{
#ifdef CONFIG_IP_ROUTE_MULTIPATH
- if (res->fi && res->fi->fib_nhs > 1)
+ if (res->fi && res->fi->fib_nhs > 1) {
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+ if (skb)
+ flowi4_set_flow_hash((struct flowi4 *)fl4,
+ skb_get_hash(skb));
+ fib_select_multipath_for_flow(res, fl4);
+#else
fib_select_multipath(res);
#endif
+ }
+#endif
/* create a routing cache entry */
return __mkroute_input(skb, res, in_dev, daddr, saddr, tos);
@@ -2170,7 +2178,11 @@ struct rtable *__ip_route_output_key(struct net
*net, struct flowi4 *fl4)
#ifdef CONFIG_IP_ROUTE_MULTIPATH
if (res.fi->fib_nhs > 1 && fl4->flowi4_oif == 0)
+#ifdef CONFIG_IP_FLOW_BASED_MULTIPATH
+ fib_select_multipath_for_flow(&res, fl4);
+#else
fib_select_multipath(&res);
+#endif
else
#endif
if (!res.prefixlen &&
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