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igmp: hash a hash table to speedup ip_check_mc_rcu()

Browse source 
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 <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Tested-by: Shawn Bohrer <[email protected]>
Reviewed-by: Cong Wang <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Eric Dumazet 2013-06-07 08:48:57 -07:00 • committed by David S. Miller
commit e989707135
4 changed files with 77 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

1
net/ipv4/devinet.c
View file

@ -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

73
net/ipv4/igmp.c
View file

@ -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;