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

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Message-id: <8C5DF277-320D-4DEB-A133-EEC301DE58DC@comsys.rwth-aachen.de>
Date:	Thu, 19 May 2011 08:52:10 +0200
From:	Alexander Zimmermann <alexander.zimmermann@...sys.rwth-aachen.de>
To:	tsuna <tsunanet@...il.com>
Cc:	David Miller <davem@...emloft.net>, kuznet@....inr.ac.ru,
	pekkas@...core.fi, jmorris@...ei.org, yoshfuji@...ux-ipv6.org,
	kaber@...sh.net, hagen@...u.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 08:42 schrieb tsuna:

> On Wed, May 18, 2011 at 11:36 PM, Alexander Zimmermann
> <alexander.zimmermann@...sys.rwth-aachen.de> wrote:
>> If you set the initRTO=0.1s, it's good for me but bad for the rest of the
>> world. That's the difference.
>> 
>> Or do you want to implement a lower barrier of 1sec so that you can ensure
>> that nobody set the initRTO lower than 1s?
> 
> Oh, I see.  Yes, there is a lower bound (and an upper bound) on what
> values the kernel will accept as initRTO.  In the patch "Implement a
> two-level initial RTO as per draft RFC 2988bis-02" above, I re-used
> TCP_RTO_MIN and TCP_RTO_MAX in net/ipv4/sysctl_net_ipv4.c in order to
> prevent users from setting a minRTO that's outside this range.  They
> are defined as follows in tcp.h:
> 
> #define TCP_RTO_MAX     ((unsigned)(120*HZ))
> #define TCP_RTO_MIN     ((unsigned)(HZ/5))
> 
> So we're talking about a [200ms ; 120s] range no matter what.

Why is 200ms a valid lower bound for initRTO? I'm aware of
measurements that 1s is save for Internet, but I don't know of any
studies that 200ms is save... 

> 
> -- 
> Benoit "tsuna" Sigoure
> Software Engineer @ www.StumbleUpon.com

//
// Dipl.-Inform. Alexander Zimmermann
// Department of Computer Science, Informatik 4
// RWTH Aachen University
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