netdev - Re: TCP delayed ACK heuristic

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Date:	Wed, 19 Dec 2012 14:54:39 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Eric Dumazet <erdnetdev@...il.com>
Cc:	netdev@...r.kernel.org, Ben Greear <greearb@...delatech.com>,
	David Miller <davem@...emloft.net>,
	Stephen Hemminger <shemminger@...tta.com>,
	Rick Jones <rick.jones2@...com>, Thomas Graf <tgraf@...hat.com>
Subject: Re: TCP delayed ACK heuristic

On Tue, 2012-12-18 at 08:30 -0800, Eric Dumazet wrote:
>  
> 
> ACKS might also be delayed because of bidirectional traffic, and is more
> controlled by the application response time. TCP stack can not easily
> estimate it.

So we still need a knob?

> 
> If you focus on bulk receive, LRO/GRO should already lower number of
> ACKS to an acceptable level and without major disruption.

Indeed.

> 
> Stretch acks are not only the receiver concern, there are issues for the
> sender that you cannot always control/change.
> 
> I recommend reading RFC2525 2.13
> 

Very helpful information!

On the sender's side, it needs to "notify" the receiver not to send
stretch acks when it is in slow-start. But I think the receiver can
detect slow-start too on its own side (based one the window size?).

Thanks!

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