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

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Message-ID: <BANLkTinBm0C4ZVE=M98AtsF--y03p4Hafg@mail.gmail.com>
Date:	Thu, 19 May 2011 19:01:53 -0700
From:	"H.K. Jerry Chu" <hkjerry.chu@...il.com>
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, hkchu@...gle.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tcp: Expose the initial RTO via a new sysctl.

On Wed, May 18, 2011 at 12:40 PM, tsuna <tsunanet@...il.com> wrote:
> On Wed, May 18, 2011 at 12:26 PM, David Miller <davem@...emloft.net> wrote:
>> If you read the ietf draft that reduces the initial RTO down to 1
>> second, it states that if we take a timeout during the initial
>> connection handshake then we have to revert the RTO back up to 3
>> seconds.
>>
>> This fallback logic conflicts with being able to only change the
>> initial RTO via sysctl, I think.  Because there are actually two
>> values at stake and they depend upon eachother, the initial RTO and
>> the value we fallback to on initial handshake retransmissions.
>>
>> So I'd rather get a patch that implements the 1 second initial
>> RTO with the 3 second fallback on SYN retransmit, than this patch.
>>
>> We already have too many knobs.
>
> I was hoping this knob would be accepted because this is such an
> important issue that it even warrants an IETF draft to attempt to
> change the standard.  I'm not sure how long it will take for this
> draft to be accepted and then implemented, so I thought adding this
> simple knob today would really help in the future.

As one of the co-authors of rfc2988bis I was planning to provide a patch
as soon as the draft gets approved but it looks like you have beaten
me to it :)

Personally I'm in favor of a knob too. We at Google has added such a
knob for years.

Jerry

>
> Plus, should the draft be accepted, this knob will still be just as
> useful (e.g. to revert back to today's behavior), and people might
> want to consider adding another knob for the fallback initRTO (this is
> debatable).  I don't believe this knob conflicts with the proposed
> change to the standard, it actually goes along with it pretty well and
> helps us prepare better for this upcoming change.
>
> I agree that there are too many knobs, and I hate feature creep too,
> but I've found many of these knobs to be really useful, and the degree
> to which Linux's TCP stack can be tuned is part of what makes it so
> versatile.
>
> --
> Benoit "tsuna" Sigoure
> Software Engineer @ www.StumbleUpon.com
> --
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