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

From: tsuna <tsunanet@gmail.com>
To: Hagen Paul Pfeifer <hagen@jauu.net>
Cc: Alexander Zimmermann <alexander.zimmermann@comsys.rwth-aachen.de>,
	David Miller <davem@davemloft.net>,
	kuznet@ms2.inr.ac.ru, pekkas@netcore.fi, jmorris@namei.org,
	yoshfuji@linux-ipv6.org, kaber@trash.net, eric.dumazet@gmail.com,
	netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tcp: Implement a two-level initial RTO as per draft RFC 2988bis-02.
Date: Thu, 19 May 2011 09:40:09 -0700	[thread overview]
Message-ID: <BANLkTimSZEbnNVzi3UvBFndHp25S0ow7YQ@mail.gmail.com> (raw)
In-Reply-To: <ef84de89c2597793d4cca5eee446ba90@localhost>

On Thu, May 19, 2011 at 1:02 AM, Hagen Paul Pfeifer <hagen@jauu.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