netdev - Re: [PATCH v9 net-next 04/15] tcp: AccECN core

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CANn89iKLKzvkLkPY67286+dKC4fGS3VtP_YhL00BmS6-0yXKxQ@mail.gmail.com>
Date: Mon, 23 Jun 2025 09:13:59 -0700
From: Eric Dumazet <edumazet@...gle.com>
To: chia-yu.chang@...ia-bell-labs.com
Cc: pabeni@...hat.com, linux-doc@...r.kernel.org, corbet@....net, 
	horms@...nel.org, dsahern@...nel.org, kuniyu@...zon.com, bpf@...r.kernel.org, 
	netdev@...r.kernel.org, dave.taht@...il.com, jhs@...atatu.com, 
	kuba@...nel.org, stephen@...workplumber.org, xiyou.wangcong@...il.com, 
	jiri@...nulli.us, davem@...emloft.net, andrew+netdev@...n.ch, 
	donald.hunter@...il.com, ast@...erby.net, liuhangbin@...il.com, 
	shuah@...nel.org, linux-kselftest@...r.kernel.org, ij@...nel.org, 
	ncardwell@...gle.com, koen.de_schepper@...ia-bell-labs.com, 
	g.white@...lelabs.com, ingemar.s.johansson@...csson.com, 
	mirja.kuehlewind@...csson.com, cheshire@...le.com, rs.ietf@....at, 
	Jason_Livingood@...cast.com, vidhi_goel@...le.com, 
	Olivier Tilmans <olivier.tilmans@...ia.com>
Subject: Re: [PATCH v9 net-next 04/15] tcp: AccECN core

On Sat, Jun 21, 2025 at 12:37 PM <chia-yu.chang@...ia-bell-labs.com> wrote:
>
> From: Ilpo Järvinen <ij@...nel.org>
>
> This change implements Accurate ECN without negotiation and
> AccECN Option (that will be added by later changes). Based on
> AccECN specifications:
>   https://tools.ietf.org/id/draft-ietf-tcpm-accurate-ecn-28.txt
>
> Accurate ECN allows feeding back the number of CE (congestion
> experienced) marks accurately to the sender in contrast to
> RFC3168 ECN that can only signal one marks-seen-yes/no per RTT.
> Congestion control algorithms can take advantage of the accurate
> ECN information to fine-tune their congestion response to avoid
> drastic rate reduction when only mild congestion is encountered.
>
> With Accurate ECN, tp->received_ce (r.cep in AccECN spec) keeps
> track of how many segments have arrived with a CE mark. Accurate
> ECN uses ACE field (ECE, CWR, AE) to communicate the value back
> to the sender which updates tp->delivered_ce (s.cep) based on the
> feedback. This signalling channel is lossy when ACE field overflow
> occurs.
>
> Conservative strategy is selected here to deal with the ACE
> overflow, however, some strategies using the AccECN option later
> in the overall patchset mitigate against false overflows detected.
>
> The ACE field values on the wire are offset by
> TCP_ACCECN_CEP_INIT_OFFSET. Delivered_ce/received_ce count the
> real CE marks rather than forcing all downstream users to adapt
> to the wire offset.
>
> This patch uses the first 1-byte hole and the last 4-byte hole of
> the tcp_sock_write_txrx for 'received_ce_pending' and 'received_ce'.
> Also, the group size of tcp_sock_write_txrx is increased from
> 91 + 4 to 95 + 4 due to the new u32 received_ce member. Below are
> the trimmed pahole outcomes before and after this patch.
>

> Signed-off-by: Ilpo Järvinen <ij@...nel.org>
> Co-developed-by: Olivier Tilmans <olivier.tilmans@...ia.com>
> Signed-off-by: Olivier Tilmans <olivier.tilmans@...ia.com>
> Co-developed-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
> Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>
>
> ---
> v9:
> - Use tcp_data_ecn_check() to set TCP_ECN_SEE flag only for RFC3168 ECN
> - Add comments about setting TCP_ECN_SEEN flag for RFC3168 and Accruate ECN

Reviewed-by: Eric Dumazet <edumazet@...gle.com>