netdev - Re: [PATCH 2.6.22] TCP: Make TCP_RTO

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Message-ID: <20070712141203.7350429a@freepuppy.rosehill.hemminger.net>
Date:	Thu, 12 Jul 2007 14:12:03 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	noboru.obata.ar@...achi.com
Cc:	David Miller <davem@...emloft.net>, yoshfuji@...ux-ipv6.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH 2.6.22] TCP: Make TCP_RTO_MAX a variable (take 2)

On Thu, 12 Jul 2007 13:24:48 -0700 (PDT)
David Miller <davem@...emloft.net> wrote:

> From: OBATA Noboru <noboru.obata.ar@...achi.com>
> Date: Thu, 12 Jul 2007 22:59:50 +0900 (JST)
> 
> > How do you think TCP timeouts in Linux can adapt to such changes
> > in network environment?
> 
> I'm honestly not interested in discussing this any more
> and Ian has even showed that the RFCs state that if we have
> a maximum it must be at least 60.
> 
> So really, there is no chance of merging a TCP_RTO_MAX
> decreasing patch, sorry.

One question is why the RTO gets so large that it limits failover?

If Linux TCP is working correctly,  RTO should be srtt + 2*rttvar

So either there is a huge srtt or variance, or something is going
wrong with RTT estimation.  Given some reasonable maximums of
Srtt = 500ms and rttvar = 250ms, that would cause RTO to be 1second.



-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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