netdev - Re: Modifying the exponential backoff on new connection SYN packets

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Message-ID: <1365523418.3887.149.camel@edumazet-glaptop>
Date:	Tue, 09 Apr 2013 09:03:38 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ed W <lists@...dgooses.com>
Cc:	Linux Networking Developer Mailing List <netdev@...r.kernel.org>
Subject: Re: Modifying the exponential backoff on new connection SYN packets

On Tue, 2013-04-09 at 16:52 +0100, Ed W wrote:
> On 09/04/2013 16:12, Eric Dumazet wrote:
> > On Tue, 2013-04-09 at 06:48 -0700, Eric Dumazet wrote:
> >
> >> You'll have to change inet_csk_reqsk_queue_prune() in
> >> net/ipv4/inet_connection_sock.c
> >>
> >> timeo = min(timeout << req->num_timeout, max_rto);
> >> req->expires = now + timeo;
> >>
> >> Good luck !
> > Oh well, this code is for SYNACK retransmits...
> >
> > For other retransmits, you'll have to take a look in
> > net/ipv4/tcp_timer.c, around lines 475
> >
> > icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
> >
> >
> 
> Hmm, I don't necessarily want to change the normal data timeouts, just 
> the initial SYN timeouts. How might I make detect that I'm in SYN state 
> and cap the timer appropriately? Apologies for beginner questions...

You'll have to add a test on :

if (sk->sk_state == TCP_SYN_SENT)

should be pretty easy.



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