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

From: H.K. Jerry Chu
Date: Thu May 19 2011 - 22:03:22 EST

On Wed, May 18, 2011 at 12:40 PM, tsuna <tsunanet@xxxxxxxxx> wrote:
> On Wed, May 18, 2011 at 12:26 PM, David Miller <davem@xxxxxxxxxxxxx> 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.


> 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 @
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