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authorDaniel Borkmann <dborkman@redhat.com>2014-01-15 16:25:34 +0100
committerDavid S. Miller <davem@davemloft.net>2014-01-16 16:17:11 -0800
commit902fefb82ef72a50c78cb4a20cc954b037a98d1c (patch)
treed6cd83b38438a03d52a3fbbcba382f51cfd6511f /net/packet
parentec48a7879e4bd9b95a076c7e999d4c3bd7093554 (diff)
packet: improve socket create/bind latency in some cases
Most people acquire PF_PACKET sockets with a protocol argument in the socket call, e.g. libpcap does so with htons(ETH_P_ALL) for all its sockets. Most likely, at some point in time a subsequent bind() call will follow, e.g. in libpcap with ... memset(&sll, 0, sizeof(sll)); sll.sll_family = AF_PACKET; sll.sll_ifindex = ifindex; sll.sll_protocol = htons(ETH_P_ALL); ... as arguments. What happens in the kernel is that already in socket() syscall, we install a proto hook via register_prot_hook() if our protocol argument is != 0. Yet, in bind() we're almost doing the same work by doing a unregister_prot_hook() with an expensive synchronize_net() call in case during socket() the proto was != 0, plus follow-up register_prot_hook() with a bound device to it this time, in order to limit traffic we get. In the case when the protocol and user supplied device index (== 0) does not change from socket() to bind(), we can spare us doing the same work twice. Similarly for re-binding to the same device and protocol. For these scenarios, we can decrease create/bind latency from ~7447us (sock-bind-2 case) to ~89us (sock-bind-1 case) with this patch. Alternatively, for the first case, if people care, they should simply create their sockets with proto == 0 argument and define the protocol during bind() as this saves a call to synchronize_net() as well (sock-bind-3 case). In all other cases, we're tied to user space behaviour we must not change, also since a bind() is not strictly required. Thus, we need the synchronize_net() to make sure no asynchronous packet processing paths still refer to the previous elements of po->prot_hook. In case of mmap()ed sockets, the workflow that includes bind() is socket() -> setsockopt(<ring>) -> bind(). In that case, a pair of {__unregister, register}_prot_hook is being called from setsockopt() in order to install the new protocol receive handler. Thus, when we call bind and can skip a re-hook, we have already previously installed the new handler. For fanout, this is handled different entirely, so we should be good. Timings on an i7-3520M machine: * sock-bind-1: 89 us * sock-bind-2: 7447 us * sock-bind-3: 75 us sock-bind-1: socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP)) = 3 bind(3, {sa_family=AF_PACKET, proto=htons(ETH_P_IP), if=all(0), pkttype=PACKET_HOST, addr(0)={0, }, 20) = 0 sock-bind-2: socket(PF_PACKET, SOCK_RAW, htons(ETH_P_IP)) = 3 bind(3, {sa_family=AF_PACKET, proto=htons(ETH_P_IP), if=lo(1), pkttype=PACKET_HOST, addr(0)={0, }, 20) = 0 sock-bind-3: socket(PF_PACKET, SOCK_RAW, 0) = 3 bind(3, {sa_family=AF_PACKET, proto=htons(ETH_P_IP), if=lo(1), pkttype=PACKET_HOST, addr(0)={0, }, 20) = 0 Signed-off-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/packet')
-rw-r--r--net/packet/af_packet.c33
1 files changed, 22 insertions, 11 deletions
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 279467b74eb7..85bb38cb56fd 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2567,9 +2567,12 @@ static int packet_release(struct socket *sock)
* Attach a packet hook.
*/
-static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 protocol)
+static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 proto)
{
struct packet_sock *po = pkt_sk(sk);
+ const struct net_device *dev_curr;
+ __be16 proto_curr;
+ bool need_rehook;
if (po->fanout) {
if (dev)
@@ -2579,21 +2582,29 @@ static int packet_do_bind(struct sock *sk, struct net_device *dev, __be16 protoc
}
lock_sock(sk);
-
spin_lock(&po->bind_lock);
- unregister_prot_hook(sk, true);
- po->num = protocol;
- po->prot_hook.type = protocol;
- if (po->prot_hook.dev)
- dev_put(po->prot_hook.dev);
+ proto_curr = po->prot_hook.type;
+ dev_curr = po->prot_hook.dev;
+
+ need_rehook = proto_curr != proto || dev_curr != dev;
+
+ if (need_rehook) {
+ unregister_prot_hook(sk, true);
- po->prot_hook.dev = dev;
- po->ifindex = dev ? dev->ifindex : 0;
+ po->num = proto;
+ po->prot_hook.type = proto;
+
+ if (po->prot_hook.dev)
+ dev_put(po->prot_hook.dev);
- packet_cached_dev_assign(po, dev);
+ po->prot_hook.dev = dev;
+
+ po->ifindex = dev ? dev->ifindex : 0;
+ packet_cached_dev_assign(po, dev);
+ }
- if (protocol == 0)
+ if (proto == 0 || !need_rehook)
goto out_unlock;
if (!dev || (dev->flags & IFF_UP)) {