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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>
This commit is contained in:
Eric Dumazet 2009-10-06 17:28:29 -07:00 committed by David S. Miller
parent bd32cafc47
commit bcdce7195e
2 changed files with 5 additions and 1 deletions
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3
include/net/sock.h
View File

@ -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);
}

3
net/socket.c
View File

@ -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);
}