netdev - RE: [PATCH v7 net-next 2/2] tcp: switch rtt estimations to usec resolution

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D0F6CC846@AcuExch.aculab.com>
Date:	Thu, 27 Feb 2014 09:57:30 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Rick Jones' <rick.jones2@...com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Eric Dumazet <eric.dumazet@...il.com>
CC:	David Miller <davem@...emloft.net>, Julian Anastasov <ja@....bg>,
	"Yuchung Cheng" <ycheng@...gle.com>,
	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>,
	Larry Brakmo <brakmo@...gle.com>
Subject: RE: [PATCH v7 net-next 2/2] tcp: switch rtt estimations to usec
 resolution

From: Rick Jones
> On 02/26/2014 05:09 PM, Stephen Hemminger wrote:
> > Since srtt is scaled by 8 and is 32 bits, This does reduce the maximum
> > possible RTT to 8 minutes or so. Which is fine, just wanted it to be
> > noted.
> 
> I have encountered some situations recently, admittedly very
> pathological, where the RTT through a VPN connection was measured in
> minutes.  I don't think it got as high as 8 minutes, but it did get as
> high as three or so.  Also mentioned only for the record.

RFC 1149 anyone :-)

I've also seen 20 minute ping responses (a long time ago).
Mind you that was a pathologically broken test senario and all sorts
of things conspired to delay the traffic.

	David



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