netdev - TCP_DELACK_MIN vs TCP_ATO

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Date:	Wed, 21 Sep 2011 15:59:54 +0300
From:	Daniel Baluta <daniel.baluta@...il.com>
To:	netdev@...r.kernel.org,
	kernelnewbies <kernelnewbies@...nelnewbies.org>
Subject: TCP_DELACK_MIN vs TCP_ATO_MIN

Hello,

RFC2582, Section 4.2 says:

"... an ACK SHOULD be generated for at least every second
full-sized segment, and MUST be generated within 500 ms
of the arrival of the first unacknowledged packet. ".

I guess that the delayed ACK timeout is computed in tcp_send_delayed_ack:

===
void tcp_send_delayed_ack(struct sock *sk)
{
        struct inet_connection_sock *icsk = inet_csk(sk);
        int ato = icsk->icsk_ack.ato;
        unsigned long timeout;

       /* .... */
        /* Stay within the limit we were given */
        timeout = jiffies + ato;
====

Can one explain what is the difference between TCP_DELACK_MIN and
TCP_ATO_MIN, specifically if the timeout (ato) is always in the interval
[TCP_DELACK_MIN, TCP_DELACK_MAX] ?

I want to make the delayed ack timeout configurable as some guys tried
here [1],
so for this reason I plan to make TCP_DELACK_MIN and TCP_DELACK_MAX
tunable via proc entries.

thanks,
Daniel.

[1] http://kerneltrap.org/mailarchive/linux-netdev/2008/9/9/3245554
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