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由 Eric Dumazet 提交于
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: NEric Dumazet <eric.dumazet@gmail.com> Signed-off-by: NDavid S. Miller <davem@davemloft.net>
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