netdev - Re: [PATCH] tcp: Implement a two-level initial RTO as per draft RFC 2988bis-02.

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Date:	Thu, 19 May 2011 18:55:59 +0200
From:	Alexander Zimmermann <alexander.zimmermann@...sys.rwth-aachen.de>
To:	tsuna <tsunanet@...il.com>
Cc:	Hagen Paul Pfeifer <hagen@...u.net>,
	David Miller <davem@...emloft.net>, kuznet@....inr.ac.ru,
	pekkas@...core.fi, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, eric.dumazet@...il.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tcp: Implement a two-level initial RTO as per draft RFC
 2988bis-02.


Am 19.05.2011 um 18:40 schrieb tsuna:

> On Thu, May 19, 2011 at 1:02 AM, Hagen Paul Pfeifer <hagen@...u.net> wrote:
>> So yes, it CAN be wise to choose other lower/upper bounds. But keep in
>> mind that we should NOT artificial limit ourself. I can image data center
>> scenarios where a initial RTO of <1 match perfectly.
> 
> Yes that's exactly the point I was trying to make when talking to
> Alexander offline.  On today's Internet, RTTs are easily in the
> hundreds of ms, and initRTO is 3s, so there's 2 orders of magnitude of
> difference.  In my environment,

Exactly. This is the point. It's *your* environment. However, TCP is
general purpose. And for the wider internet 1s is know to be save. See the
measurements in the draft that Mark Allman run.

> if my RTT is ~2µs, an initRTO of 200ms
> means that there's a gap of 6 orders of magnitude (!).

Currently, initRTO is 3s. So you the gap is even larger. 

> And yes,
> although I don't work for High Frequency Trading companies in Wall
> Street, I'm already buying switches full of line-rate 10Gb ports with
> a port-to-port latency of 500ns for L2/L3 forwarding/switching.  I
> expect this kind of network gear will quickly become prevalent in
> datacenter/backend environments.
> 
> -- 
> Benoit "tsuna" Sigoure
> Software Engineer @ www.StumbleUpon.com

//
// Dipl.-Inform. Alexander Zimmermann
// Department of Computer Science, Informatik 4
// RWTH Aachen University
// Ahornstr. 55, 52056 Aachen, Germany
// phone: (49-241) 80-21422, fax: (49-241) 80-22222
// email: zimmermann@...rwth-aachen.de
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