From 2b85a34e911bf483c27cfdd124aeb1605145dc80 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Thu, 11 Jun 2009 02:55:43 -0700 Subject: [PATCH] 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 Signed-off-by: David S. Miller --- include/net/sock.h | 6 +++++- net/core/sock.c | 29 +++++++++++++++++++++++++---- net/ipv4/ip_output.c | 1 - net/ipv6/ip6_output.c | 1 - 4 files changed, 30 insertions(+), 7 deletions(-) diff --git a/include/net/sock.h b/include/net/sock.h index 4bb1ff9fd15b..010e14a93c92 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1217,9 +1217,13 @@ static inline int skb_copy_to_page(struct sock *sk, char __user *from, static inline void skb_set_owner_w(struct sk_buff *skb, struct sock *sk) { - sock_hold(sk); skb->sk = sk; skb->destructor = sock_wfree; + /* + * We used to take a refcount on sk, but following operation + * is enough to guarantee sk_free() wont free this sock until + * all in-flight packets are completed + */ atomic_add(skb->truesize, &sk->sk_wmem_alloc); } diff --git a/net/core/sock.c b/net/core/sock.c index 04e35eb2e736..06e26b77ad9e 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 9248d2807ba6..247026282669 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 db6c7224a862..7c76e3d18215 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; -- GitLab