From: Eric Dumazet <[email protected]> Hosts sending lot of ACK packets exhibit high sock_wfree() cost because of cache line miss to test SOCK_USE_WRITE_QUEUE
We could move this flag close to sk_wmem_alloc but it is better to perform the atomic_sub_and_test() on a clean cache line, as it avoid one extra bus transaction. skb_orphan_partial() can also have a fast track for packets that either are TCP acks, or already went through another skb_orphan_partial() Signed-off-by: Eric Dumazet <[email protected]> --- include/net/sock.h | 1 + net/core/sock.c | 24 ++++++++++++++++++++++++ net/ipv4/tcp_output.c | 2 +- 3 files changed, 26 insertions(+), 1 deletion(-) diff --git a/include/net/sock.h b/include/net/sock.h index 3df778ccaa820b00b4038feedae30cd444e9a212..9be2ffb4b8fcf54cc9c8bd73628dd7572b1d783d 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -1434,6 +1434,7 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority); struct sk_buff *sock_wmalloc(struct sock *sk, unsigned long size, int force, gfp_t priority); +void __sock_wfree(struct sk_buff *skb); void sock_wfree(struct sk_buff *skb); void skb_orphan_partial(struct sk_buff *skb); void sock_rfree(struct sk_buff *skb); diff --git a/net/core/sock.c b/net/core/sock.c index e16a5db853c6f455b0ac826744d0ee5e96a44863..e1151f11eb4aa0a5afa95bfee9d00a85c4d50af6 100644 --- a/net/core/sock.c +++ b/net/core/sock.c @@ -1655,6 +1655,17 @@ void sock_wfree(struct sk_buff *skb) } EXPORT_SYMBOL(sock_wfree); +/* This variant of sock_wfree() is used by TCP, + * since it sets SOCK_USE_WRITE_QUEUE. + */ +void __sock_wfree(struct sk_buff *skb) +{ + struct sock *sk = skb->sk; + + if (atomic_sub_and_test(skb->truesize, &sk->sk_wmem_alloc)) + __sk_free(sk); +} + void skb_set_owner_w(struct sk_buff *skb, struct sock *sk) { skb_orphan(skb); @@ -1677,8 +1688,21 @@ void skb_set_owner_w(struct sk_buff *skb, struct sock *sk) } EXPORT_SYMBOL(skb_set_owner_w); +/* This helper is used by netem, as it can hold packets in its + * delay queue. We want to allow the owner socket to send more + * packets, as if they were already TX completed by a typical driver. + * But we also want to keep skb->sk set because some packet schedulers + * rely on it (sch_fq for example). So we set skb->truesize to a small + * amount (1) and decrease sk_wmem_alloc accordingly. + */ void skb_orphan_partial(struct sk_buff *skb) { + /* If this skb is a TCP pure ACK or already went here, + * we have nothing to do. 2 is already a very small truesize. + */ + if (skb->truesize <= 2) + return; + /* TCP stack sets skb->ooo_okay based on sk_wmem_alloc, * so we do not completely orphan skb, but transfert all * accounted bytes but one, to avoid unexpected reorders. diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c index 1a487ff95d4c0572737e4f972666229f12ef1e08..778ac8f2d84be389478e4d92335e1979482b3817 100644 --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -949,7 +949,7 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it, skb_orphan(skb); skb->sk = sk; - skb->destructor = skb_is_tcp_pure_ack(skb) ? sock_wfree : tcp_wfree; + skb->destructor = skb_is_tcp_pure_ack(skb) ? __sock_wfree : tcp_wfree; skb_set_hash_from_sk(skb, sk); atomic_add(skb->truesize, &sk->sk_wmem_alloc);
