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Date: Thu, 22 Mar 2012 16:13:57 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Vincent Li <vincent.mc.li@...il.com> Cc: netdev@...r.kernel.org Subject: Re: Piggyback the final ACK of the three way TCP connection establishment with the data On Thu, 2012-03-22 at 16:02 -0700, Vincent Li wrote: > > > > No kernel patch is needed, you already can do this on linux. > > > > Check file net/ipv4/tcp_input.c lines around 5722 > > > > > > is this code snippet in tcp_rcv_synsent_state_process that you refer to? > > 5676 if (sk->sk_write_pending || > 5677 icsk->icsk_accept_queue.rskq_defer_accept || > 5678 icsk->icsk_ack.pingpong) { > 5679 /* Save one ACK. Data will be ready after > 5680 * several ticks, if write_pending is set. > 5681 * > 5682 * It may be deleted, but with this > feature tcpdumps > 5683 * look so _wonderfully_ clever, that I > was not able > 5684 * to stand against the temptation 8) --ANK > 5685 */ > 5686 inet_csk_schedule_ack(sk); > 5687 icsk->icsk_ack.lrcvtime = tcp_time_stamp; > 5688 icsk->icsk_ack.ato = TCP_ATO_MIN; > 5689 tcp_incr_quickack(sk); > 5690 tcp_enter_quickack_mode(sk); > 5691 inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK, > 5692 TCP_DELACK_MAX, > TCP_RTO_MAX); > 5693 > 5694 discard: > 5695 __kfree_skb(skb); > 5696 return 0; > 5697 } else { > 5698 tcp_send_ack(sk); > 5699 } > > if I understand it correct on linux, the application code need to set > socket option with TCP_DEFER_ACCEPT or TCP_QUICKACK in order to > trigger it, correct? > > We have user running wu-ftpd on HP Unix with tcp tunable > tcp_delay_final_twh_ack on. so in active FTP situation, when wu-ftpd > open up data connection to client, it sends SYN, client SYN/ACK, then > ACK/PUSH with data. so on HU UNIX, it appears just turn on tcp tunable > tcp_delay_final_twh_ack would make it happen. > > but on Linux, do I need to change wu-ftpd code and modify the socket > option with TCP_DEFER_ACCEPT or TCP_QUICKACK in order to trigger the > code snippet in tcp_rcv_synsent_state_process? Yes. A third possibility (reading the code) if you use non blocking IO, is to send() a message right after connect() -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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