Re: [tcpm] [EXTERNAL] Re: Linux doesn’t implement RFC3465

Yoshifumi Nishida <nsd.ietf@gmail.com> Mon, 09 August 2021 17:07 UTC

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From: Yoshifumi Nishida <nsd.ietf@gmail.com>
Date: Mon, 9 Aug 2021 10:07:13 -0700
Message-ID: <CAAK044Q5APha_+8Q-EsyGTKb2d0_1Zjhtn8h-O0iHFQ7jVSCMw@mail.gmail.com>
To: Neal Cardwell <ncardwell@google.com>
Cc: Yuchung Cheng <ycheng=40google.com@dmarc.ietf.org>, Vidhi Goel <vidhi_goel@apple.com>, "tcpm@ietf.org" <tcpm@ietf.org>, "mallman@icir.org" <mallman@icir.org>
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Subject: Re: [tcpm] =?utf-8?q?=5BEXTERNAL=5D_Re=3A_Linux_doesn=E2=80=99t_impl?= =?utf-8?q?ement_RFC3465?=
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Yes, that was my intention. Sorry for being unclear.
I thought updating RFC5681 could be impactful. So, if it would happen, I
would like to make sure we won't have another update for a long time.
--
Yoshi

On Mon, Aug 9, 2021 at 9:53 AM Neal Cardwell <ncardwell@google.com> wrote:

> I think Yoshifumi is suggesting that if the WG re-spins  RFC5681 then in
> addition to folding in discussion of ABC/RFC3465 the RFC5681bis could also
> include the IW10 content in RFC6928. That could help save time in avoiding
> promoting RFC6928 from experimental to proposed standard.
>
> That sounds reasonable to me as well. Although the initial window is a
> somewhat independent issue that might evolve independently from the
> congestion algorithm itself, so I can imagine advantages to keeping it
> separate.
>
> neal
>
>
> On Mon, Aug 9, 2021 at 12:39 PM Yuchung Cheng <ycheng=
> 40google.com@dmarc.ietf.org> wrote:
>
>> Sorry I don't understand your suggestion. Is that related to ABC? could
>> you explain more
>>
>> On Mon, Aug 9, 2021 at 1:41 AM Yoshifumi Nishida <nsd.ietf@gmail.com>
>> wrote:
>>
>>> I don't have a strong opinion on this yet, But, if we *could* move in
>>> this direction, it might be good to think about the IW explanation in
>>> RFC5681 as well?
>>> if we do this, we might not need to discuss promoting RFC6928.
>>> --
>>> Yoshi
>>>
>>> On Sat, Aug 7, 2021 at 7:57 AM Neal Cardwell <ncardwell=
>>> 40google.com@dmarc.ietf.org> wrote:
>>>
>>>> I also agree with Yuchung’s suggestion, for all of the reasons he
>>>> provided.
>>>>
>>>> best,
>>>> neal
>>>>
>>>>
>>>> On Fri, Aug 6, 2021 at 3:59 PM Vidhi Goel <vidhi_goel=
>>>> 40apple.com@dmarc.ietf.org> wrote:
>>>>
>>>>> I agree with Yuchung’s suggestion for all the reasons he provided. And
>>>>> its better to have it at one place.
>>>>>
>>>>> Vidhi
>>>>>
>>>>> On Aug 6, 2021, at 12:53 PM, Yuchung Cheng <
>>>>> ycheng=40google.com@dmarc.ietf.org> wrote:
>>>>>
>>>>> Hi WG
>>>>>
>>>>> I have been wondering if we (= IETF) should just update RFC5681
>>>>> directly, instead of another RFC3465-bis with experimental status.
>>>>>
>>>>> Appropriate byte counting is essential but the RFC5681 of L=1 is
>>>>> detrimental. There are far more people who read RFC5681 to implement the
>>>>> new stack instead of RFC3465. So we should fold the experimental RFC3465
>>>>> updates into RFC5681 directly, and obsolete RFC3465.
>>>>>
>>>>> This is orthogonal to the final value of L :-)
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> On Tue, Aug 3, 2021 at 9:42 AM Yuchung Cheng <ycheng@google.com>
>>>>> wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>> On Mon, Aug 2, 2021 at 6:12 PM Yuchung Cheng <ycheng@google.com>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Mon, Aug 2, 2021 at 5:53 PM Neal Cardwell <ncardwell=
>>>>>>> 40google.com@dmarc.ietf.org> wrote:
>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Mon, Aug 2, 2021 at 8:46 PM Praveen Balasubramanian <pravb=
>>>>>>>> 40microsoft.com@dmarc.ietf.org> wrote:
>>>>>>>>
>>>>>>>>> In experiments a few years ago on DC networks, values over L=8
>>>>>>>>> resulted in a noticeable increase in packet drops and retransmissions
>>>>>>>>> (without pacing). Windows TCP has been using L=8 for many years now. If we
>>>>>>>>> do want to specify a fallback L value for implementations that cannot pace,
>>>>>>>>> my suggestion would be to use the value 8.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Neal, are there cases where Linux is or can be deployed with
>>>>>>>>> infinite L and no pacing?
>>>>>>>>>
>>>>>>>>
>>>>>>>> Yes, "infinite L and no pacing" is the default behavior for Linux
>>>>>>>> TCP, starting in 2013 for slow-start and then starting in 2015 for
>>>>>>>> congestion avoidance.
>>>>>>>>
>>>>>>> To be more clear: both fq_pacing and TCP pacing have been disabled
>>>>>>> by default in Linux upstream. We do not know how much Linux senders enable
>>>>>>> them today besides the Google servers.
>>>>>>>
>>>>>>> Regarding L = 8, to avoid another round of why or why not. We could
>>>>>>> say inf-L causes line-rate burst up to the stretched ACK degree so put a
>>>>>>> comfortable L if you prefer, then mention implementation practice like
>>>>>>> yours. At the end of the day it's ad-hoc (or "art") and subject to change.
>>>>>>> It might be sensible to cap at cwnd to disincentivize receivers /
>>>>>>> middle-boxes bunching up 10 rounds of ACKs.
>>>>>>>
>>>>>> Sorry please ignore my previous message about the cwnd cap. It is
>>>>>> completely unnecessary -- since with ack-clocking and appropriate counting,
>>>>>> a correct sender would never release more than a cwnd-worth of data. I was
>>>>>> imagining the multiple application-limited burst could let the receiver
>>>>>> keep holding up ACKs, but that can never exceed a cwnd worth of data.
>>>>>>
>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>>> Yuchung pasted the URLs for the exact Linux commits above, which
>>>>>>>> are:
>>>>>>>>
>>>>>>>>
>>>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9f9843a751d0a2057f9f3d313886e7e5e6ebaac9
>>>>>>>>
>>>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9cd981dcf174d26805a032aefa791436da709bee
>>>>>>>>
>>>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c22bdca94782f05b9337d8548bde51b2f38ef17f
>>>>>>>>
>>>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=814d488c61260521b1b3cc97063700a5a6667c8f
>>>>>>>>
>>>>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e73ebb0881ea5534ce606c1d71b4ac44db5c6930
>>>>>>>>
>>>>>>>> But I understand that not everyone is in a position to read
>>>>>>>> GPL-licensed code. :-)
>>>>>>>>
>>>>>>>> best regards,
>>>>>>>> neal
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> *From:* tcpm <tcpm-bounces@ietf.org> *On Behalf Of * Neal Cardwell
>>>>>>>>> *Sent:* Monday, August 2, 2021 4:18 PM
>>>>>>>>> *To:* Vidhi Goel <vidhi_goel@apple.com>
>>>>>>>>> *Cc:* Extensions <tcpm@ietf.org>rg>; Mark Allman <mallman@icir.org>
>>>>>>>>> *Subject:* [EXTERNAL] Re: [tcpm] Linux doesn’t implement RFC3465
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Mon, Aug 2, 2021 at 7:02 PM Vidhi Goel <vidhi_goel@apple.com>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Mon, Aug 2, 2021 at 3:37 PM Mark Allman <mallman@icir.org>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> > The fact is that Linux CC has long moved to infinite L since
>>>>>>>>> 2031,
>>>>>>>>>
>>>>>>>>> So, if our experience is with L=\infinity and it is demonstrably OK
>>>>>>>>> why don't we say *THAT* instead of "make L=5 or L=10"?  I would
>>>>>>>>> submit that it makes more sense to leverage experience than it
>>>>>>>>> does
>>>>>>>>>
>>>>>>>>> to make things up.
>>>>>>>>>
>>>>>>>>> +1
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Yes, I agree that would be a great approach to take.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> So, we are saying it is fine to ignore L completely and simply
>>>>>>>>> increase cwnd by bytes_acked during slow start? And if this causes large
>>>>>>>>> bursts to be sent out (when an implementation doesn’t do pacing), that is
>>>>>>>>> fine?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Yes, I think that is the proposal on the table, and it sounds good
>>>>>>>>> to me.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> A rationale would be:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> (1) Implementations SHOULD pace (RFC 7661).
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> (2) Implementations that don't pace will generally be causing
>>>>>>>>> large bursts for many different reasons anyway (data and/or ACK aggregation
>>>>>>>>> in the network or end hosts), restart from idle,...) so having a constant L
>>>>>>>>> does not provide enough protection from bursts to justify the cost in
>>>>>>>>> reduced performance (in the form of slower slow-start). In support of this,
>>>>>>>>> experience with this as the default behavior in Linux TCP over the
>>>>>>>>> 2013-2021 period suggests this works well enough in practice.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> neal
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> tcpm mailing list
>>>>>>>> tcpm@ietf.org
>>>>>>>> https://www.ietf.org/mailman/listinfo/tcpm
>>>>>>>>
>>>>>>> _______________________________________________
>>>>> tcpm mailing list
>>>>> tcpm@ietf.org
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>>>>>
>>>>>
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