netdev - RE: TCP delayed ACK heuristic

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Message-ID: <1356007270.25310.20.camel@cr0>
Date:	Thu, 20 Dec 2012 20:41:10 +0800
From:	Cong Wang <amwang@...hat.com>
To:	David Laight <David.Laight@...LAB.COM>
Cc:	David Miller <davem@...emloft.net>, rick.jones2@...com,
	netdev@...r.kernel.org, greearb@...delatech.com,
	eric.dumazet@...il.com, shemminger@...tta.com, tgraf@...hat.com
Subject: RE: TCP delayed ACK heuristic

On Thu, 2012-12-20 at 09:57 +0000, David Laight wrote:
> > So, can we at least have a sysctl to control the timeout of the delayed
> > ACK? I mean the minimum 40ms. TCP_QUICKACK can help too, but it requires
> > the receiver to modify the application and has to be set every time when
> > calling recv().
> 
> A sysctl in inappropriate - it affects the entire TCP protocol stack.
> 
> You want different behaviour for different remote hosts (probably
> different subnets).
> In particular your local subnet is unlikely to have packet loss
> and very likely to have a very low RTT.
> 
> AFAICT a lot of the recent 'tuning' has been done for web/ftp
> servers that are very remote from the client. These connections
> are also request-response ones - quite often with large responses.
> 
> IMHO This has been to the detriment of local connections.
> 

A customer prefers faster response in their low-loss environment, 40ms
is not good. Of course, they are supposed to know their environment when
they tune this.

Or maybe a sysctl equals to TCP_QUICKACK?


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