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

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Message-ID: <BANLkTimSZEbnNVzi3UvBFndHp25S0ow7YQ@mail.gmail.com>
Date:	Thu, 19 May 2011 09:40:09 -0700
From:	tsuna <tsunanet@...il.com>
To:	Hagen Paul Pfeifer <hagen@...u.net>
Cc:	Alexander Zimmermann <alexander.zimmermann@...sys.rwth-aachen.de>,
	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.

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