igmp: hash a hash table to speedup ip_check_mc_rcu()

After IP route cache removal, multicast applications using
a lot of multicast addresses hit a O(N) behavior in ip_check_mc_rcu()

Add a per in_device hash table to get faster lookup.

This hash table is created only if the number of items in mc_list is
above 4.

Reported-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Shawn Bohrer <sbohrer@rgmadvisors.com>
Reviewed-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

2 files changed, 71 insertions, 3 deletions

diff --git a/net/ipv4/devinet.c b/net/ipv4/devinet.c
index b047e2d8a614..3469506c106d 100644
--- a/net/ipv4/devinet.c
+++ b/net/ipv4/devinet.c
@@ -215,6 +215,7 @@ void in_dev_finish_destroy(struct in_device *idev)
 
         WARN_ON(idev->ifa_list);
         WARN_ON(idev->mc_list);
+        kfree(rcu_dereference_protected(idev->mc_hash, 1));
 #ifdef NET_REFCNT_DEBUG
         pr_debug("%s: %p=%s\n", __func__, idev, dev ? dev->name : "NIL");
 #endif
diff --git a/net/ipv4/igmp.c b/net/ipv4/igmp.c
index 450f625361e4..f72011df9c59 100644
--- a/net/ipv4/igmp.c
+++ b/net/ipv4/igmp.c
@@ -1217,6 +1217,57 @@ static void igmp_group_added(struct ip_mc_list *im)
  *      Multicast list managers
  */
 
+static u32 ip_mc_hash(const struct ip_mc_list *im)
+{
+        return hash_32((u32)im->multiaddr, MC_HASH_SZ_LOG);
+}
+
+static void ip_mc_hash_add(struct in_device *in_dev,
+                           struct ip_mc_list *im)
+{
+        struct ip_mc_list __rcu **mc_hash;
+        u32 hash;
+
+        mc_hash = rtnl_dereference(in_dev->mc_hash);
+        if (mc_hash) {
+                hash = ip_mc_hash(im);
+                im->next_hash = rtnl_dereference(mc_hash[hash]);
+                rcu_assign_pointer(mc_hash[hash], im);
+                return;
+        }
+
+        /* do not use a hash table for small number of items */
+        if (in_dev->mc_count < 4)
+                return;
+
+        mc_hash = kzalloc(sizeof(struct ip_mc_list *) << MC_HASH_SZ_LOG,
+                          GFP_KERNEL);
+        if (!mc_hash)
+                return;
+
+        for_each_pmc_rtnl(in_dev, im) {
+                hash = ip_mc_hash(im);
+                im->next_hash = rtnl_dereference(mc_hash[hash]);
+                RCU_INIT_POINTER(mc_hash[hash], im);
+        }
+
+        rcu_assign_pointer(in_dev->mc_hash, mc_hash);
+}
+
+static void ip_mc_hash_remove(struct in_device *in_dev,
+                              struct ip_mc_list *im)
+{
+        struct ip_mc_list __rcu **mc_hash = rtnl_dereference(in_dev->mc_hash);
+        struct ip_mc_list *aux;
+
+        if (!mc_hash)
+                return;
+        mc_hash += ip_mc_hash(im);
+        while ((aux = rtnl_dereference(*mc_hash)) != im)
+                mc_hash = &aux->next_hash;
+        *mc_hash = im->next_hash;
+}
+
 
 /*
  *      A socket has joined a multicast group on device dev.
@@ -1258,6 +1309,8 @@ void ip_mc_inc_group(struct in_device *in_dev, __be32 addr)
         in_dev->mc_count++;
         rcu_assign_pointer(in_dev->mc_list, im);
 
+        ip_mc_hash_add(in_dev, im);
+
 #ifdef CONFIG_IP_MULTICAST
         igmpv3_del_delrec(in_dev, im->multiaddr);
 #endif
@@ -1314,6 +1367,7 @@ void ip_mc_dec_group(struct in_device *in_dev, __be32 addr)
              ip = &i->next_rcu) {
                 if (i->multiaddr == addr) {
                         if (--i->users == 0) {
+                                ip_mc_hash_remove(in_dev, i);
                                 *ip = i->next_rcu;
                                 in_dev->mc_count--;
                                 igmp_group_dropped(i);
@@ -2321,12 +2375,25 @@ void ip_mc_drop_socket(struct sock *sk)
 int ip_check_mc_rcu(struct in_device *in_dev, __be32 mc_addr, __be32 src_addr, u16 proto)
 {
         struct ip_mc_list *im;
+        struct ip_mc_list __rcu **mc_hash;
         struct ip_sf_list *psf;
         int rv = 0;
 
-        for_each_pmc_rcu(in_dev, im) {
-                if (im->multiaddr == mc_addr)
-                        break;
+        mc_hash = rcu_dereference(in_dev->mc_hash);
+        if (mc_hash) {
+                u32 hash = hash_32((u32)mc_addr, MC_HASH_SZ_LOG);
+
+                for (im = rcu_dereference(mc_hash[hash]);
+                     im != NULL;
+                     im = rcu_dereference(im->next_hash)) {
+                        if (im->multiaddr == mc_addr)
+                                break;
+                }
+        } else {
+                for_each_pmc_rcu(in_dev, im) {
+                        if (im->multiaddr == mc_addr)
+                                break;
+                }
         }
         if (im && proto == IPPROTO_IGMP) {
                 rv = 1;