netdev - Re: [PATCH] tcp: account SYN-ACK timeouts & retransmissions

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Message-Id: <201001132307.59472.opurdila@ixiacom.com>
Date:	Wed, 13 Jan 2010 23:07:59 +0200
From:	Octavian Purdila <opurdila@...acom.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, mpyatkovskiy@...acom.com
Subject: Re: [PATCH] tcp: account SYN-ACK timeouts & retransmissions

On Tuesday 12 January 2010 18:55:31 you wrote:
> On Tuesday 12 January 2010 02:15:37 you wrote:
> > From: Octavian Purdila <opurdila@...acom.com>
> > Date: Tue, 12 Jan 2010 00:16:33 +0200
> >
> > > On Friday 08 January 2010 03:25:07 you wrote:
> > >> From: Octavian Purdila <opurdila@...acom.com>
> > >> Date: Wed,  6 Jan 2010 22:10:58 +0200
> > >>
> > >> > Signed-off-by: Maksim Pyatkovskiy <mpyatkovskiy@...acom.com>
> > >> > Signed-off-by: Octavian Purdila <opurdila@...acom.com>
> > >>
> > >> RETRANSSEGS is meant to count data segments retransmits, not pure
> > >> control frames.
> > >>
> > >> Similarly for TCPTIMEOUTS, it's mean for data retransmit timeouts.
> > >>
> > >> If you overload these statistics with other similar events, they
> > >> become less meaningful.
> > >
> > > But we do increment RETRANSSEGS & TCPTIMEOUTS for SYNs. This creates an
> > > imbalance in client/server stats which makes things harder to diagnose.
> >
> > Interesting.
> >
> > Can you do me a favor and look into the code history and see
> > if we used to account both sides?
> 
> Sure.

I think we lost the SynAck accounting with this commit from the netdev-vger-
cvs tree, where tcp_syn_recv_timer was introduced:

commit 2248761e5cfcb8687563b29c77064185e7604947
Author: davem <davem>
Date:   Sun Nov 10 21:25:00 1996 +0000

    Merge to 2.1.8, IPV6 is here.  Also fix
    a stupid bug in the kernel unaligned trap handler
    where st %g0, [foo] would fail miserably.


Before this, both Syns and SynAcks seems to be accounted for.
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