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

From: tsuna <tsunanet@gmail.com>
To: Alexander Zimmermann <alexander.zimmermann@comsys.rwth-aachen.de>
Cc: David Miller <davem@davemloft.net>,
	kuznet@ms2.inr.ac.ru, pekkas@netcore.fi, jmorris@namei.org,
	yoshfuji@linux-ipv6.org, kaber@trash.net, hagen@jauu.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: Wed, 18 May 2011 23:42:30 -0700	[thread overview]
Message-ID: <BANLkTiku9KTHCm59cib5KY8mz0ewSLsHFQ@mail.gmail.com> (raw)
In-Reply-To: <C70B920C-6176-481B-B6D2-E52769291EBC@comsys.rwth-aachen.de>

On Wed, May 18, 2011 at 11:36 PM, Alexander Zimmermann
<alexander.zimmermann@comsys.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.

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