Commit bcdce719 authored Oct 06, 2009 by Eric Dumazet Committed by David S. Miller Oct 06, 2009

net: speedup sk_wake_async()

An incoming datagram must bring into cpu cache *lot* of cache lines,
in particular : (other parts omitted (hash chains, ip route cache...))

On 32bit arches :

offsetof(struct sock, sk_rcvbuf) =0x30 (read)
offsetof(struct sock, sk_lock) =0x34 (rw)

offsetof(struct sock, sk_sleep) =0x50 (read)
offsetof(struct sock, sk_rmem_alloc) =0x64 (rw)
offsetof(struct sock, sk_receive_queue)=0x74 (rw)

offsetof(struct sock, sk_forward_alloc)=0x98 (rw)

offsetof(struct sock, sk_callback_lock)=0xcc (rw)
offsetof(struct sock, sk_drops) =0xd8 (read if we add dropcount support, rw if frame dropped)
offsetof(struct sock, sk_filter) =0xf8 (read)

offsetof(struct sock, sk_socket) =0x138 (read)

offsetof(struct sock, sk_data_ready) =0x15c (read)

We can avoid sk->sk_socket and socket->fasync_list referencing on sockets
with no fasync() structures. (socket->fasync_list ptr is probably already in cache
because it shares a cache line with socket->wait, ie location pointed by sk->sk_sleep)

This avoids one cache line load per incoming packet for common cases (no fasync())

We can leave (or even move in a future patch) sk->sk_socket in a cold location

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent bd32cafc

include/net/sock.h

+2 −1

Original line number	Diff line number	Diff line
		@@ -504,6 +504,7 @@ enum sock_flags {
		SOCK_TIMESTAMPING_SOFTWARE, /* %SOF_TIMESTAMPING_SOFTWARE */
		SOCK_TIMESTAMPING_RAW_HARDWARE, /* %SOF_TIMESTAMPING_RAW_HARDWARE */
		SOCK_TIMESTAMPING_SYS_HARDWARE, /* %SOF_TIMESTAMPING_SYS_HARDWARE */
		SOCK_FASYNC, /* fasync() active */
		};

		static inline void sock_copy_flags(struct sock nsk, struct sock osk)
		@@ -1396,7 +1397,7 @@ static inline unsigned long sock_wspace(struct sock *sk)

		static inline void sk_wake_async(struct sock *sk, int how, int band)
		{
		if (sk->sk_socket && sk->sk_socket->fasync_list)
		if (sock_flag(sk, SOCK_FASYNC))
		sock_wake_async(sk->sk_socket, how, band);
		}

net/socket.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -1100,11 +1100,14 @@ static int sock_fasync(int fd, struct file *filp, int on)
		fna->fa_next = sock->fasync_list;
		write_lock_bh(&sk->sk_callback_lock);
		sock->fasync_list = fna;
		sock_set_flag(sk, SOCK_FASYNC);
		write_unlock_bh(&sk->sk_callback_lock);
		} else {
		if (fa != NULL) {
		write_lock_bh(&sk->sk_callback_lock);
		*prev = fa->fa_next;
		if (!sock->fasync_list)
		sock_reset_flag(sk, SOCK_FASYNC);
		write_unlock_bh(&sk->sk_callback_lock);
		kfree(fa);
		}