netdev - Re: [PATCH v5 net-next 08/13] gso: AccECN support

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Message-ID: <CANn89i+wgm3DQafFygTQgqwX8p7AGmrBz1b0nocejrw-=xnhDQ@mail.gmail.com>
Date: Thu, 7 Nov 2024 13:41:48 +0100
From: Eric Dumazet <edumazet@...gle.com>
To: chia-yu.chang@...ia-bell-labs.com
Cc: netdev@...r.kernel.org, dsahern@...il.com, davem@...emloft.net, 
	dsahern@...nel.org, pabeni@...hat.com, joel.granados@...nel.org, 
	kuba@...nel.org, andrew+netdev@...n.ch, horms@...nel.org, pablo@...filter.org, 
	kadlec@...filter.org, netfilter-devel@...r.kernel.org, coreteam@...filter.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
Subject: Re: [PATCH v5 net-next 08/13] gso: AccECN support

On Tue, Nov 5, 2024 at 11:07 AM <chia-yu.chang@...ia-bell-labs.com> wrote:
>
> From: Ilpo Järvinen <ij@...nel.org>
>
> Handling the CWR flag differs between RFC 3168 ECN and AccECN.
> With RFC 3168 ECN aware TSO (NETIF_F_TSO_ECN) CWR flag is cleared
> starting from 2nd segment which is incompatible how AccECN handles
> the CWR flag. Such super-segments are indicated by SKB_GSO_TCP_ECN.
> With AccECN, CWR flag (or more accurately, the ACE field that also
> includes ECE & AE flags) changes only when new packet(s) with CE
> mark arrives so the flag should not be changed within a super-skb.
> The new skb/feature flags are necessary to prevent such TSO engines
> corrupting AccECN ACE counters by clearing the CWR flag (if the
> CWR handling feature cannot be turned off).
>
> If NIC is completely unaware of RFC3168 ECN (doesn't support
> NETIF_F_TSO_ECN) or its TSO engine can be set to not touch CWR flag
> despite supporting also NETIF_F_TSO_ECN, TSO could be safely used
> with AccECN on such NIC. This should be evaluated per NIC basis
> (not done in this patch series for any NICs).
>
> For the cases, where TSO cannot keep its hands off the CWR flag,
> a GSO fallback is provided by this patch.
>
> Signed-off-by: Ilpo Järvinen <ij@...nel.org>
> Signed-off-by: Chia-Yu Chang <chia-yu.chang@...ia-bell-labs.com>

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