linux-kernel - Re: [PATCH] tcp: Expose the initial RTO via a new sysctl.

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Message-ID: <BANLkTi=p1V1x+y=-cH-Q7bvueu_4_D1ywQ@mail.gmail.com>
Date:	Fri, 20 May 2011 17:06:01 -0700
From:	"H.K. Jerry Chu" <hkjerry.chu@...il.com>
To:	Hagen Paul Pfeifer <hagen@...u.net>
Cc:	David Miller <davem@...emloft.net>, tsunanet@...il.com,
	kuznet@....inr.ac.ru, pekkas@...core.fi, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tcp: Expose the initial RTO via a new sysctl.

Hey Hagen,

On Fri, May 20, 2011 at 4:00 AM, Hagen Paul Pfeifer <hagen@...u.net> wrote:
>
> On Fri, 20 May 2011 03:27:37 -0700, "H.K. Jerry Chu" wrote:
>
> Hi Jerry
>
>> Not sure how our various parameter tuning proposals deviate from the
> "TCP
>> over everything" principle?
>
> For our environment it hurts because we _always_ have an initial RTO >1. I
> understand and accept that 98% will benefit of this modification, no doubt
> Jerry! Try to put yourself in our situation: imaging a proposal of an init

Understood but my point was none of the parameter tuning proposals break
"TCP over everything", although they may not help solving "TCP optimized for
everything", but we never had the latter anyway.

We've tried hard to keep the penalty to those initRTT > 1sec paths at a minimum,
i.e., just one extra tinygram. This is important also for us because it may take
> 1sec for many Android clients to establish connections over a radio channel that
has been put into power saving mode.

> RTO modification to 0.5 seconds. Maybe because 98% of Internet traffic is
> now localized and the RTO is average now 0.2 seconds. Anyway, this will
> penalize your network always and this will be the situation for one of my
> customer. I can live with that, I see the benefits for the rest of the
> world. But I am happy to see a knob where I can restore the old behavior.
> Maybe some other environments will benefit from a even lower or higher
> initial RTO.

Yep, that's why we've had a knob for this for years.

Jerry

>
> Hagen
>
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