ipv4: L3 hash-based multipath

Replaces the per-packet multipath with a hash-based multipath using
source and destination address.

Signed-off-by: Peter Nørlund <pch@ordbogen.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/ip_fib.h b/include/net/ip_fib.h
index 727d6e9a96856b4fde184a188e1aec003ed4bfa9..7a51fd8d99e45d6e019dc0e4ff89267050974a9f 100644 (file)
--- a/include/net/ip_fib.h
+++ b/include/net/ip_fib.h
@@ -79,7 +79,7 @@ struct fib_nh {
        unsigned char           nh_scope;
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
        int                     nh_weight;
-       int                     nh_power;
+       atomic_t                nh_upper_bound;
 #endif
 #ifdef CONFIG_IP_ROUTE_CLASSID
        __u32                   nh_tclassid;
@@ -118,7 +118,7 @@ struct fib_info {
 #define fib_advmss fib_metrics[RTAX_ADVMSS-1]
        int                     fib_nhs;
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
-       int                     fib_power;
+       int                     fib_weight;
 #endif
        struct rcu_head         rcu;
        struct fib_nh           fib_nh[0];
@@ -320,7 +320,15 @@ int ip_fib_check_default(__be32 gw, struct net_device *dev);
 int fib_sync_down_dev(struct net_device *dev, unsigned long event);
 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);
+
+extern u32 fib_multipath_secret __read_mostly;
+
+static inline int fib_multipath_hash(__be32 saddr, __be32 daddr)
+{
+       return jhash_2words(saddr, daddr, fib_multipath_secret) >> 1;
+}
+
+void fib_select_multipath(struct fib_result *res, int hash);
 
 /* Exported by fib_trie.c */
 void fib_trie_init(void);

diff --git a/net/ipv4/fib_semantics.c b/net/ipv4/fib_semantics.c
index 064bd3caaa4f1f8fda928d0c1e3ca2446d67c2ed..0c49d2f3bbc0ebecdb313d098c31694f5822bb7b 100644 (file)
--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -57,8 +57,7 @@ static unsigned int fib_info_cnt;
 static struct hlist_head fib_info_devhash[DEVINDEX_HASHSIZE];
 
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
-
-static DEFINE_SPINLOCK(fib_multipath_lock);
+u32 fib_multipath_secret __read_mostly;
 
 #define for_nexthops(fi) {                                             \
        int nhsel; const struct fib_nh *nh;                             \
@@ -532,7 +531,67 @@ errout:
        return ret;
 }
 
-#endif
+static void fib_rebalance(struct fib_info *fi)
+{
+       int total;
+       int w;
+       struct in_device *in_dev;
+
+       if (fi->fib_nhs < 2)
+               return;
+
+       total = 0;
+       for_nexthops(fi) {
+               if (nh->nh_flags & RTNH_F_DEAD)
+                       continue;
+
+               in_dev = __in_dev_get_rcu(nh->nh_dev);
+
+               if (in_dev &&
+                   IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev) &&
+                   nh->nh_flags & RTNH_F_LINKDOWN)
+                       continue;
+
+               total += nh->nh_weight;
+       } endfor_nexthops(fi);
+
+       w = 0;
+       change_nexthops(fi) {
+               int upper_bound;
+
+               in_dev = __in_dev_get_rcu(nexthop_nh->nh_dev);
+
+               if (nexthop_nh->nh_flags & RTNH_F_DEAD) {
+                       upper_bound = -1;
+               } else if (in_dev &&
+                          IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev) &&
+                          nexthop_nh->nh_flags & RTNH_F_LINKDOWN) {
+                       upper_bound = -1;
+               } else {
+                       w += nexthop_nh->nh_weight;
+                       upper_bound = DIV_ROUND_CLOSEST(2147483648LL * w,
+                                                       total) - 1;
+               }
+
+               atomic_set(&nexthop_nh->nh_upper_bound, upper_bound);
+       } endfor_nexthops(fi);
+
+       net_get_random_once(&fib_multipath_secret,
+                           sizeof(fib_multipath_secret));
+}
+
+static inline void fib_add_weight(struct fib_info *fi,
+                                 const struct fib_nh *nh)
+{
+       fi->fib_weight += nh->nh_weight;
+}
+
+#else /* CONFIG_IP_ROUTE_MULTIPATH */
+
+#define fib_rebalance(fi) do { } while (0)
+#define fib_add_weight(fi, nh) do { } while (0)
+
+#endif /* CONFIG_IP_ROUTE_MULTIPATH */
 
 static int fib_encap_match(struct net *net, u16 encap_type,
                           struct nlattr *encap,
@@ -1094,8 +1153,11 @@ struct fib_info *fib_create_info(struct fib_config *cfg)
 
        change_nexthops(fi) {
                fib_info_update_nh_saddr(net, nexthop_nh);
+               fib_add_weight(fi, nexthop_nh);
        } endfor_nexthops(fi)
 
+       fib_rebalance(fi);
+
 link_it:
        ofi = fib_find_info(fi);
        if (ofi) {
@@ -1317,12 +1379,6 @@ int fib_sync_down_dev(struct net_device *dev, unsigned long event)
                                        nexthop_nh->nh_flags |= RTNH_F_LINKDOWN;
                                        break;
                                }
-#ifdef CONFIG_IP_ROUTE_MULTIPATH
-                               spin_lock_bh(&fib_multipath_lock);
-                               fi->fib_power -= nexthop_nh->nh_power;
-                               nexthop_nh->nh_power = 0;
-                               spin_unlock_bh(&fib_multipath_lock);
-#endif
                                dead++;
                        }
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
@@ -1345,6 +1401,8 @@ int fib_sync_down_dev(struct net_device *dev, unsigned long event)
                        }
                        ret++;
                }
+
+               fib_rebalance(fi);
        }
 
        return ret;
@@ -1467,20 +1525,15 @@ int fib_sync_up(struct net_device *dev, unsigned int nh_flags)
                            !__in_dev_get_rtnl(dev))
                                continue;
                        alive++;
-#ifdef CONFIG_IP_ROUTE_MULTIPATH
-                       spin_lock_bh(&fib_multipath_lock);
-                       nexthop_nh->nh_power = 0;
-                       nexthop_nh->nh_flags &= ~nh_flags;
-                       spin_unlock_bh(&fib_multipath_lock);
-#else
                        nexthop_nh->nh_flags &= ~nh_flags;
-#endif
                } endfor_nexthops(fi)
 
                if (alive > 0) {
                        fi->fib_flags &= ~nh_flags;
                        ret++;
                }
+
+               fib_rebalance(fi);
        }
 
        return ret;
@@ -1488,62 +1541,19 @@ int fib_sync_up(struct net_device *dev, unsigned int nh_flags)
 
 #ifdef CONFIG_IP_ROUTE_MULTIPATH
 
-/*
- * The algorithm is suboptimal, but it provides really
- * fair weighted route distribution.
- */
-void fib_select_multipath(struct fib_result *res)
+void fib_select_multipath(struct fib_result *res, int hash)
 {
        struct fib_info *fi = res->fi;
-       struct in_device *in_dev;
-       int w;
-
-       spin_lock_bh(&fib_multipath_lock);
-       if (fi->fib_power <= 0) {
-               int power = 0;
-               change_nexthops(fi) {
-                       in_dev = __in_dev_get_rcu(nexthop_nh->nh_dev);
-                       if (nexthop_nh->nh_flags & RTNH_F_DEAD)
-                               continue;
-                       if (in_dev &&
-                           IN_DEV_IGNORE_ROUTES_WITH_LINKDOWN(in_dev) &&
-                           nexthop_nh->nh_flags & RTNH_F_LINKDOWN)
-                               continue;
-                       power += nexthop_nh->nh_weight;
-                       nexthop_nh->nh_power = nexthop_nh->nh_weight;
-               } endfor_nexthops(fi);
-               fi->fib_power = power;
-               if (power <= 0) {
-                       spin_unlock_bh(&fib_multipath_lock);
-                       /* Race condition: route has just become dead. */
-                       res->nh_sel = 0;
-                       return;
-               }
-       }
-
 
-       /* w should be random number [0..fi->fib_power-1],
-        * it is pretty bad approximation.
-        */
-
-       w = jiffies % fi->fib_power;
+       for_nexthops(fi) {
+               if (hash > atomic_read(&nh->nh_upper_bound))
+                       continue;
 
-       change_nexthops(fi) {
-               if (!(nexthop_nh->nh_flags & RTNH_F_DEAD) &&
-                   nexthop_nh->nh_power) {
-                       w -= nexthop_nh->nh_power;
-                       if (w <= 0) {
-                               nexthop_nh->nh_power--;
-                               fi->fib_power--;
-                               res->nh_sel = nhsel;
-                               spin_unlock_bh(&fib_multipath_lock);
-                               return;
-                       }
-               }
+               res->nh_sel = nhsel;
+               return;
        } endfor_nexthops(fi);
 
        /* Race condition: route has just become dead. */
        res->nh_sel = 0;
-       spin_unlock_bh(&fib_multipath_lock);
 }
 #endif

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 76ca4e75f7853b52c1a17fc824752382b2595bd5..0cca44476b1e6339ea9a187db66cc1c9df5bdc15 100644 (file)
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -1658,8 +1658,12 @@ 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)
-               fib_select_multipath(res);
+       if (res->fi && res->fi->fib_nhs > 1) {
+               int h;
+
+               h = fib_multipath_hash(saddr, daddr);
+               fib_select_multipath(res, h);
+       }
 #endif
 
        /* create a routing cache entry */
@@ -2189,8 +2193,12 @@ 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)
-               fib_select_multipath(&res);
+       if (res.fi->fib_nhs > 1 && fl4->flowi4_oif == 0) {
+               int h;
+
+               h = fib_multipath_hash(fl4->saddr, fl4->daddr);
+               fib_select_multipath(&res, h);
+       }
        else
 #endif
        if (!res.prefixlen &&