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[45.32.91.63]) by smtp.gmail.com with ESMTPSA id f14-20020a170902684e00b0017b69f99321sm605901pln.219.2022.11.10.21.14.59 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Thu, 10 Nov 2022 21:15:01 -0800 (PST) From: Zhenlei Huang Message-Id: <63BD8E79-29FA-47E6-BBF7-B755BA060FC7@gmail.com> Content-Type: multipart/alternative; boundary="Apple-Mail=_31C73F77-BFEF-4968-AFBB-394C2135F9F6" List-Id: Networking and TCP/IP with FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-net List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-net@freebsd.org Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.7\)) Subject: Re: Too aggressive TCP ACKs Date: Fri, 11 Nov 2022 13:14:56 +0800 In-Reply-To: Cc: Hans Petter Selasky , Michael Tuexen , "freebsd-net@freebsd.org" To: "Scheffenegger, Richard" References: <75D35F36-7759-4168-ADBA-C2414F5B53BC@gmail.com> <712641B3-5196-40CC-9B64-04637F16F649@lurchi.franken.de> <62A0DD30-B3ED-48BE-9C01-146487599092@gmail.com> <0FED34A9-D093-442A-83B7-08C06D11F8B5@lurchi.franken.de> <330A9146-F7CC-4CAB-9003-2F90B872AC3E@gmail.com> <1ed66217-5463-fd4d-7e7a-58d9981bc44c@selasky.org> <5A501643-1E81-4A8C-8DDC-094371DC03D7@gmail.com> <7EDD65B7-5FCD-42E1-A9E8-AA5139B0A81E@gmail.com> X-Mailer: Apple Mail (2.3608.120.23.2.7) X-Rspamd-Queue-Id: 4N7n2b4R39z412h X-Spamd-Bar: ---- X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[]; ASN(0.00)[asn:15169, ipnet:2607:f8b0::/32, country:US]; TAGGED_FROM(0.00)[] X-ThisMailContainsUnwantedMimeParts: N --Apple-Mail=_31C73F77-BFEF-4968-AFBB-394C2135F9F6 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Nov 10, 2022, at 8:01 PM, Scheffenegger, Richard = wrote: >=20 > This is the current draft in this space: > =20 > https://datatracker.ietf.org/doc/draft-gomez-tcpm-ack-rate-request/ = > =20 > and it has been adopted as WG document at this weeks IETF, from what I = can tell. Thanks for that information ! > =20 > So it has traction =E2=80=93 if you want to give your feedback, please = subscribe to the tcpm mailing list, and discuss your use case and how/if = the approach aligns with this there. Subscribed. > =20 > Richard > =20 > =20 > =20 > From: owner-freebsd-net@freebsd.org = > On Behalf Of Zhenlei Huang > Sent: Donnerstag, 10. November 2022 09:07 > To: Hans Petter Selasky > > Cc: Michael Tuexen >; freebsd-net@freebsd.org = > Subject: Re: Too aggressive TCP ACKs > =20 > NetApp Security WARNING: This is an external email. Do not click links = or open attachments unless you recognize the sender and know the content = is safe.=20 >=20 >=20 >=20 > On Nov 9, 2022, at 11:18 AM, Zhenlei Huang > wrote: > =20 > =20 > On Oct 22, 2022, at 6:14 PM, Hans Petter Selasky > wrote: > =20 > Hi, >=20 > Some thoughts about this topic. > =20 > Sorry for late response. >=20 >=20 >=20 > Delaying ACKs means loss of performance when using Gigabit TCP = connections in data centers. There it is important to ACK the data as = quick as possible, to avoid running out of TCP window space. Thinking = about TCP connections at 30 GBit/s and above! > =20 > In data centers, the bandwidth is much more and the latency is = extremely low (compared to WAN), sub-milliseconds . > The TCP window space is bandwidth multiply RTT. For a 30 GBit/s = network it is about 750KiB . I think that is trivial for a > datacenter server. >=20 >=20 > 4.2.3.2 in RFC 1122 states: > > in a stream of full-sized segments there SHOULD be an ACK for at = least every second segment=20 > Even if the ACK every tenth segment, the impact of delayed ACKs on TCP = window is not significant ( at most > ten segments not ACKed in TCP send window ). > =20 > Anyway, for datacenter usage the bandwidth is symmetric and the = reverse path ( TX path of receiver ) is sufficient. > Servers can even ACK every segment (no delaying ACK). > =20 >=20 > I think the implementation should be exactly like it is. >=20 > There is a software LRO in FreeBSD to coalesce the ACKs before they = hit the network stack, so there are no real problems there. > =20 > I'm OK with the current implementation. > =20 > I think upper layers (or application) have (business) information to = indicate whether delaying ACKs should be employed. > After googling I found there's a draft [1]. > =20 > [1] Sender Control of Delayed Acknowledgments in TCP: = https://www.ietf.org/archive/id/draft-gomez-tcpm-delack-suppr-reqs-01.xml = > =20 > Found the html / pdf / txt version of the draft RFC. > https://datatracker.ietf.org/doc/draft-gomez-tcpm-ack-pull/ = >=20 >=20 >=20 >=20 >=20 > --HPS >=20 >=20 > =20 > Best regards, > Zhenlei --Apple-Mail=_31C73F77-BFEF-4968-AFBB-394C2135F9F6 Content-Transfer-Encoding: quoted-printable Content-Type: text/html; charset=utf-8
On = Nov 10, 2022, at 8:01 PM, Scheffenegger, Richard <Richard.Scheffenegger@netapp.com> wrote:

This is the current draft in this space:
 
https://datatracker.ietf.org/doc/draft-gomez-tcpm-ack-rate-requ= est/
 
and it has been = adopted as WG document at this weeks IETF, from what I can = tell.

Thanks for that information !

 
So it has = traction =E2=80=93 if you want to give your feedback, please subscribe = to the tcpm mailing list, and discuss your use case and how/if the = approach aligns with this = there.

Subscribed.

 
Richard
 
 
 
From: owner-freebsd-net@freebsd.org <owner-freebsd-net@freebsd.org> On Behalf = Of Zhenlei = Huang
Sent: Donnerstag, 10. November = 2022 09:07
To: Hans Petter Selasky <hps@selasky.org>
Cc: Michael Tuexen <michael.tuexen@lurchi.franken.de>; freebsd-net@freebsd.org
Subject: Re: Too aggressive TCP = ACKs
 
NetApp Security WARNING: This is an external email. Do not click links or = open attachments unless you recognize the sender and know the content is = safe. 



On = Nov 9, 2022, at 11:18 AM, Zhenlei Huang <zlei.huang@gmail.com> = wrote:
 
 
On Oct 22, 2022, at 6:14 = PM, Hans Petter Selasky <hps@selasky.org> wrote:
 
Hi,

Some thoughts = about this topic.
 
Sorry = for late response.



Delaying = ACKs means loss of performance when using Gigabit TCP connections in = data centers. There it is important to ACK the data as quick as = possible, to avoid running out of TCP window space. Thinking about TCP = connections at 30 GBit/s and above!
 
In data centers, the bandwidth is much = more and the latency is extremely low (compared to = WAN), sub-milliseconds .
The TCP window space is bandwidth = multiply RTT. For a 30 GBit/s network it is about 750KiB . I think that = is trivial for a
datacenter server.


4.2.3.2 in RFC 1122 states:
> in a stream of full-sized segments there = SHOULD be an ACK for at least every second segment 
Even if = the ACK every tenth segment, the impact of delayed ACKs on TCP = window is not significant ( at most
 ten segments not ACKed in = TCP send window ).
 
Anyway, for datacenter usage = the bandwidth is symmetric and the reverse path ( TX path of = receiver ) is sufficient.
Servers can even ACK every segment = (no delaying ACK).
 

I think the implementation should = be exactly like it is.

There is a software = LRO in FreeBSD to coalesce the ACKs before they hit the network stack, = so there are no real problems there.
 
I'm OK with the current = implementation.
 
I think upper layers (or application) = have (business) information to indicate whether delaying ACKs should be = employed.
After googling I found there's a draft [1].
 
[1] Sender Control of Delayed Acknowledgments in = TCP: https://www.ietf.org/archive/id/draft-gomez-tcpm-delack-suppr-r= eqs-01.xml
 
Found = the html / pdf / txt version of the draft RFC.
https://datatracker.ietf.org/doc/draft-gomez-tcpm-ack-pull/=





--HPS

 
Best regards,
Zhenlei
<= /div>
= --Apple-Mail=_31C73F77-BFEF-4968-AFBB-394C2135F9F6--