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authorEric Dumazet <eric.dumazet@gmail.com>2009-06-11 02:55:43 -0700
committerDavid S. Miller <davem@davemloft.net>2009-06-11 02:55:43 -0700
commit2b85a34e911bf483c27cfdd124aeb1605145dc80 (patch)
tree3cea3e8a27b62de2f92e759641c27200d8bde421 /net
parentf2333a014c1e13ac8e1b73a6fd77731c524eff78 (diff)
downloadlinux-2.6.34-ux500-2b85a34e911bf483c27cfdd124aeb1605145dc80.tar.gz
net: No more expensive sock_hold()/sock_put() on each tx
One of the problem with sock memory accounting is it uses a pair of sock_hold()/sock_put() for each transmitted packet. This slows down bidirectional flows because the receive path also needs to take a refcount on socket and might use a different cpu than transmit path or transmit completion path. So these two atomic operations also trigger cache line bounces. We can see this in tx or tx/rx workloads (media gateways for example), where sock_wfree() can be in top five functions in profiles. We use this sock_hold()/sock_put() so that sock freeing is delayed until all tx packets are completed. As we also update sk_wmem_alloc, we could offset sk_wmem_alloc by one unit at init time, until sk_free() is called. Once sk_free() is called, we atomic_dec_and_test(sk_wmem_alloc) to decrement initial offset and atomicaly check if any packets are in flight. skb_set_owner_w() doesnt call sock_hold() anymore sock_wfree() doesnt call sock_put() anymore, but check if sk_wmem_alloc reached 0 to perform the final freeing. Drawback is that a skb->truesize error could lead to unfreeable sockets, or even worse, prematurely calling __sk_free() on a live socket. Nice speedups on SMP. tbench for example, going from 2691 MB/s to 2711 MB/s on my 8 cpu dev machine, even if tbench was not really hitting sk_refcnt contention point. 5 % speedup on a UDP transmit workload (depends on number of flows), lowering TX completion cpu usage. Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r--net/core/sock.c29
-rw-r--r--net/ipv4/ip_output.c1
-rw-r--r--net/ipv6/ip6_output.c1
3 files changed, 25 insertions, 6 deletions
diff --git a/net/core/sock.c b/net/core/sock.c
index 04e35eb2e73..06e26b77ad9 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1008,7 +1008,7 @@ struct sock *sk_alloc(struct net *net, int family, gfp_t priority,
}
EXPORT_SYMBOL(sk_alloc);
-void sk_free(struct sock *sk)
+static void __sk_free(struct sock *sk)
{
struct sk_filter *filter;
@@ -1031,6 +1031,17 @@ void sk_free(struct sock *sk)
put_net(sock_net(sk));
sk_prot_free(sk->sk_prot_creator, sk);
}
+
+void sk_free(struct sock *sk)
+{
+ /*
+ * We substract one from sk_wmem_alloc and can know if
+ * some packets are still in some tx queue.
+ * If not null, sock_wfree() will call __sk_free(sk) later
+ */
+ if (atomic_dec_and_test(&sk->sk_wmem_alloc))
+ __sk_free(sk);
+}
EXPORT_SYMBOL(sk_free);
/*
@@ -1071,7 +1082,10 @@ struct sock *sk_clone(const struct sock *sk, const gfp_t priority)
newsk->sk_backlog.head = newsk->sk_backlog.tail = NULL;
atomic_set(&newsk->sk_rmem_alloc, 0);
- atomic_set(&newsk->sk_wmem_alloc, 0);
+ /*
+ * sk_wmem_alloc set to one (see sk_free() and sock_wfree())
+ */
+ atomic_set(&newsk->sk_wmem_alloc, 1);
atomic_set(&newsk->sk_omem_alloc, 0);
skb_queue_head_init(&newsk->sk_receive_queue);
skb_queue_head_init(&newsk->sk_write_queue);
@@ -1175,12 +1189,18 @@ void __init sk_init(void)
void sock_wfree(struct sk_buff *skb)
{
struct sock *sk = skb->sk;
+ int res;
/* In case it might be waiting for more memory. */
- atomic_sub(skb->truesize, &sk->sk_wmem_alloc);
+ res = atomic_sub_return(skb->truesize, &sk->sk_wmem_alloc);
if (!sock_flag(sk, SOCK_USE_WRITE_QUEUE))
sk->sk_write_space(sk);
- sock_put(sk);
+ /*
+ * if sk_wmem_alloc reached 0, we are last user and should
+ * free this sock, as sk_free() call could not do it.
+ */
+ if (res == 0)
+ __sk_free(sk);
}
EXPORT_SYMBOL(sock_wfree);
@@ -1819,6 +1839,7 @@ void sock_init_data(struct socket *sock, struct sock *sk)
sk->sk_stamp = ktime_set(-1L, 0);
atomic_set(&sk->sk_refcnt, 1);
+ atomic_set(&sk->sk_wmem_alloc, 1);
atomic_set(&sk->sk_drops, 0);
}
EXPORT_SYMBOL(sock_init_data);
diff --git a/net/ipv4/ip_output.c b/net/ipv4/ip_output.c
index 9248d2807ba..24702628266 100644
--- a/net/ipv4/ip_output.c
+++ b/net/ipv4/ip_output.c
@@ -498,7 +498,6 @@ int ip_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
BUG_ON(frag->sk);
if (skb->sk) {
- sock_hold(skb->sk);
frag->sk = skb->sk;
frag->destructor = sock_wfree;
truesizes += frag->truesize;
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index db6c7224a86..7c76e3d1821 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -680,7 +680,6 @@ static int ip6_fragment(struct sk_buff *skb, int (*output)(struct sk_buff *))
BUG_ON(frag->sk);
if (skb->sk) {
- sock_hold(skb->sk);
frag->sk = skb->sk;
frag->destructor = sock_wfree;
truesizes += frag->truesize;