netdev - Re: Shaping TCP ACK packets

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Message-ID: <1323151166.2467.11.camel@edumazet-laptop>
Date:	Tue, 06 Dec 2011 06:59:26 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"John A. Sullivan III" <jsullivan@...nsourcedevel.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Shaping TCP ACK packets

Le lundi 05 décembre 2011 à 23:18 -0500, John A. Sullivan III a écrit :
> Hello, all.  I've seen several sites recommend prioritizing TCP ACK
> packets using tc.  Is that a good idea? I have two reservations:
> 
> 1) If my line is congested, isn't delaying ACKs a good way to slow
> down the conversation? Accelerating ACKs under congestion sounds a bit
> like stuffing more food in my mouth when I'm already choking.
> 
It depends which way is congested. Sites recommends prioritizing ACKS on
the up way, because most of the time ADSL links are assymetric. an
uplink is congested.


> 2) By messing with normal coordination of TCP, do I risk making a
> mess.  Specifically, can I create problems with out of order packet
> delivery - send an ACK before the packet which should have preceded
> it? I suppose in a well behaved protocol that wouldn't happen but I'm
> not sure.  Thanks - John
> --

Well, if you prioritize true acks (packets with no payload), there is no
reorder problem per se.



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