netdev - Re: [PATCH net-next 09/44] gso: AccECN support

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Message-ID: <20241015183120.72eabc79@kicinski-fedora-PC1C0HJN>
Date: Tue, 15 Oct 2024 18:31:29 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: chia-yu.chang@...ia-bell-labs.com
Cc: netdev@...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
Subject: Re: [PATCH net-next 09/44] gso: AccECN support

On Tue, 15 Oct 2024 12:29:05 +0200 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).

net/ethtool/common.c:52:35: warning: initializer overrides prior initialization of this subobject [-Winitializer-overrides]
   52 |         [NETIF_F_FCOE_CRC_BIT] =         "tx-checksum-fcoe-crc",
      |                                          ^~~~~~~~~~~~~~~~~~~~~~
net/ethtool/common.c:35:30: note: previous initialization is here
   35 |         [NETIF_F_GSO_ACCECN_BIT] =       "tx-tcp-accecn-segmentation",
      |                                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~