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udp: Use hash2 for long hash1 chains in __udp*_lib_mcast_deliver.

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Many multicast sources can have the same port which can result in a very
large list when hashing by port only. Hash by address and port instead
if this is the case. This makes multicast more similar to unicast.

On a 24-core machine receiving from 500 multicast sockets on the same
port, before this patch 80% of system CPU was used up by spin locking
and only ~25% of packets were successfully delivered.

With this patch, all packets are delivered and kernel overhead is ~8%
system CPU on spinlocks.

Signed-off-by: David Held <drheld@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
David Held
2014-07-15 23:28:32 -04:00
committed by David S. Miller
parent 5cf3d46192
commit 2dc41cff75
3 changed files with 55 additions and 20 deletions
Download Patch File Download Diff File Expand all files Collapse all files

31
net/ipv4/udp.c
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@ -1619,6 +1619,8 @@ static void flush_stack(struct sock **stack, unsigned int count,
if (skb1 && udp_queue_rcv_skb(sk, skb1) <= 0)
skb1 = NULL;
sock_put(sk);
}
if (unlikely(skb1))
kfree_skb(skb1);
@ -1651,10 +1653,20 @@ static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
unsigned short hnum = ntohs(uh->dest);
struct udp_hslot *hslot = udp_hashslot(udptable, net, hnum);
int dif = skb->dev->ifindex;
unsigned int i, count = 0;
unsigned int count = 0, offset = offsetof(typeof(*sk), sk_nulls_node);
unsigned int hash2 = 0, hash2_any = 0, use_hash2 = (hslot->count > 10);
if (use_hash2) {
hash2_any = udp4_portaddr_hash(net, htonl(INADDR_ANY), hnum) &
udp_table.mask;
hash2 = udp4_portaddr_hash(net, daddr, hnum) & udp_table.mask;
start_lookup:
hslot = &udp_table.hash2[hash2];
offset = offsetof(typeof(*sk), __sk_common.skc_portaddr_node);
}
spin_lock(&hslot->lock);
sk_nulls_for_each(sk, node, &hslot->head) {
sk_nulls_for_each_entry_offset(sk, node, &hslot->head, offset) {
if (__udp_is_mcast_sock(net, sk,
uh->dest, daddr,
uh->source, saddr,
@ -1664,24 +1676,23 @@ static int __udp4_lib_mcast_deliver(struct net *net, struct sk_buff *skb,
count = 0;
}
stack[count++] = sk;
sock_hold(sk);
}
}
/*
* before releasing chain lock, we must take a reference on sockets
*/
for (i = 0; i < count; i++)
sock_hold(stack[i]);
spin_unlock(&hslot->lock);
/* Also lookup *:port if we are using hash2 and haven't done so yet. */
if (use_hash2 && hash2 != hash2_any) {
hash2 = hash2_any;
goto start_lookup;
}
/*
* do the slow work with no lock held
*/
if (count) {
flush_stack(stack, count, skb, count - 1);
for (i = 0; i < count; i++)
sock_put(stack[i]);
} else {
kfree_skb(skb);
}