From: Eric Dumazet Date: Mon, 15 Nov 2021 19:02:46 +0000 (-0800) Subject: tcp: defer skb freeing after socket lock is released X-Git-Tag: v6.1-rc5~2306^2~443^2~3 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=f35f821935d8df76f9c92e2431a225bdff938169;p=platform%2Fkernel%2Flinux-starfive.git tcp: defer skb freeing after socket lock is released tcp recvmsg() (or rx zerocopy) spends a fair amount of time freeing skbs after their payload has been consumed. A typical ~64KB GRO packet has to release ~45 page references, eventually going to page allocator for each of them. Currently, this freeing is performed while socket lock is held, meaning that there is a high chance that BH handler has to queue incoming packets to tcp socket backlog. This can cause additional latencies, because the user thread has to process the backlog at release_sock() time, and while doing so, additional frames can be added by BH handler. This patch adds logic to defer these frees after socket lock is released, or directly from BH handler if possible. Being able to free these skbs from BH handler helps a lot, because this avoids the usual alloc/free assymetry, when BH handler and user thread do not run on same cpu or NUMA node. One cpu can now be fully utilized for the kernel->user copy, and another cpu is handling BH processing and skb/page allocs/frees (assuming RFS is not forcing use of a single CPU) Tested: 100Gbit NIC Max throughput for one TCP_STREAM flow, over 10 runs MTU : 1500 Before: 55 Gbit After: 66 Gbit MTU : 4096+(headers) Before: 82 Gbit After: 95 Gbit Signed-off-by: Eric Dumazet Signed-off-by: David S. Miller --- diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 686a666..b8b8065 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -36,6 +36,7 @@ #include #include #include +#include #include #include #if IS_ENABLED(CONFIG_NF_CONNTRACK) @@ -743,6 +744,7 @@ struct sk_buff { }; struct rb_node rbnode; /* used in netem, ip4 defrag, and tcp stack */ struct list_head list; + struct llist_node ll_node; }; union { diff --git a/include/net/sock.h b/include/net/sock.h index 2d40fe4..2578d1f 100644 --- a/include/net/sock.h +++ b/include/net/sock.h @@ -63,6 +63,7 @@ #include #include #include +#include #include #include #include @@ -408,6 +409,8 @@ struct sock { struct sk_buff *head; struct sk_buff *tail; } sk_backlog; + struct llist_head defer_list; + #define sk_rmem_alloc sk_backlog.rmem_alloc int sk_forward_alloc; diff --git a/include/net/tcp.h b/include/net/tcp.h index 05c8167..44e442b 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1368,6 +1368,16 @@ static inline bool tcp_checksum_complete(struct sk_buff *skb) } bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb); + +void __sk_defer_free_flush(struct sock *sk); + +static inline void sk_defer_free_flush(struct sock *sk) +{ + if (llist_empty(&sk->defer_list)) + return; + __sk_defer_free_flush(sk); +} + int tcp_filter(struct sock *sk, struct sk_buff *skb); void tcp_set_state(struct sock *sk, int state); void tcp_done(struct sock *sk); diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 4e70116..33cd9a1 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -1580,14 +1580,34 @@ void tcp_cleanup_rbuf(struct sock *sk, int copied) tcp_send_ack(sk); } +void __sk_defer_free_flush(struct sock *sk) +{ + struct llist_node *head; + struct sk_buff *skb, *n; + + head = llist_del_all(&sk->defer_list); + llist_for_each_entry_safe(skb, n, head, ll_node) { + prefetch(n); + skb_mark_not_on_list(skb); + __kfree_skb(skb); + } +} +EXPORT_SYMBOL(__sk_defer_free_flush); + static void tcp_eat_recv_skb(struct sock *sk, struct sk_buff *skb) { + __skb_unlink(skb, &sk->sk_receive_queue); if (likely(skb->destructor == sock_rfree)) { sock_rfree(skb); skb->destructor = NULL; skb->sk = NULL; + if (!skb_queue_empty(&sk->sk_receive_queue) || + !llist_empty(&sk->defer_list)) { + llist_add(&skb->ll_node, &sk->defer_list); + return; + } } - sk_eat_skb(sk, skb); + __kfree_skb(skb); } static struct sk_buff *tcp_recv_skb(struct sock *sk, u32 seq, u32 *off) @@ -2422,6 +2442,7 @@ static int tcp_recvmsg_locked(struct sock *sk, struct msghdr *msg, size_t len, /* Do not sleep, just process backlog. */ __sk_flush_backlog(sk); } else { + sk_defer_free_flush(sk); sk_wait_data(sk, &timeo, last); } @@ -2540,6 +2561,7 @@ int tcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock, ret = tcp_recvmsg_locked(sk, msg, len, nonblock, flags, &tss, &cmsg_flags); release_sock(sk); + sk_defer_free_flush(sk); if (cmsg_flags && ret >= 0) { if (cmsg_flags & TCP_CMSG_TS) @@ -3065,7 +3087,7 @@ int tcp_disconnect(struct sock *sk, int flags) sk->sk_frag.page = NULL; sk->sk_frag.offset = 0; } - + sk_defer_free_flush(sk); sk_error_report(sk); return 0; } @@ -4194,6 +4216,7 @@ static int do_tcp_getsockopt(struct sock *sk, int level, err = BPF_CGROUP_RUN_PROG_GETSOCKOPT_KERN(sk, level, optname, &zc, &len, err); release_sock(sk); + sk_defer_free_flush(sk); if (len >= offsetofend(struct tcp_zerocopy_receive, msg_flags)) goto zerocopy_rcv_cmsg; switch (len) { diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 5ad81bf..3dd19a2 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -2102,6 +2102,7 @@ process: sk_incoming_cpu_update(sk); + sk_defer_free_flush(sk); bh_lock_sock_nested(sk); tcp_segs_in(tcp_sk(sk), skb); ret = 0; diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index f41f14b..3b7d6ed 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -1758,6 +1758,7 @@ process: sk_incoming_cpu_update(sk); + sk_defer_free_flush(sk); bh_lock_sock_nested(sk); tcp_segs_in(tcp_sk(sk), skb); ret = 0;