netdev - Re: [RFC PATCHv5 1/5] [TCP]: Add highest_sack seqno, points to globally highest SACK

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Date:	Mon, 26 Mar 2007 00:55:57 +0300 (EEST)
From:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To:	David Miller <davem@...emloft.net>
cc:	netdev@...r.kernel.org
Subject: Re: [RFC PATCHv5 1/5] [TCP]: Add highest_sack seqno, points to
 globally highest SACK

On Sat, 24 Mar 2007, David Miller wrote:

> From: "Ilpo_Järvinen" <ilpo.jarvinen@...sinki.fi>
> Date: Fri, 16 Mar 2007 20:41:02 +0200
> 
> > It is guaranteed to be valid only when !tp->sacked_out. In most
> > cases this seqno is available in the last ACK but there is no
> > guarantee for that. The new fast recovery loss marking algorithm
> > needs this as entry point.
> 
> It's a shame we keep around multiple values which represent very
> related values.  For example, this new seqno could be computed
> using "fackets_out" if we knew also how many holes there were.

It would then be an estimate which is 100% accurate in most cases (when 
all related skbs are full sized). I think it must never underestimate 
highest_sack though, it would be quite ok to use fackets_out * mss but any 
> mss skb would obviously be a problem (if they ever occur)... Are all 
paths ok with that (this is beoynd the codepaths I'm quite sure of...)?!

-- 
 i.