From: Jakub Kicinski <kuba@kernel.org>
To: chia-yu.chang@nokia-bell-labs.com
Cc: shaojijie@huawei.com, shenjian15@huawei.com,
linux-rdma@vger.kernel.org, eperezma@redhat.com,
jasowang@redhat.com, virtualization@lists.linux.dev,
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rs.ietf@gmx.at, Jason_Livingood@comcast.com,
vidhi_goel@apple.com, Parav Pandit <parav@nvidia.com>
Subject: Re: [PATCH v5 net-next 1/2] net: update comments for SKB_GSO_TCP_ECN and SKB_GSO_TCP_ACCECN
Date: Tue, 11 Aug 2026 17:30:17 -0700 [thread overview]
Message-ID: <20260811173017.3d18dfdc@kernel.org> (raw)
In-Reply-To: <20260804213510.673084-2-chia-yu.chang@nokia-bell-labs.com>
On Tue, 4 Aug 2026 23:35:09 +0200 chia-yu.chang@nokia-bell-labs.com
wrote:
> This corresponds to discussions in virtio mailing list:
> https://lore.kernel.org/all/20250814120118.81787-1-chia-yu.chang@nokia-bell-labs.com/
> And it was suggested to clarify SKB_GSO_TCP_ECN and SKB_GSO_TCP_ACCECN.
> - /* This indicates the tcp segment has CWR set. */
> + /* For TX, this indicates that the first TCP segment has CWR set, and
> + * any subsequent segment in the same skb has CWR cleared. This flag
> + * must not be used in RX, because the connection to which the segment
> + * belongs is not tracked to use RFC3168 or AccECN. Using RFC3168 ECN
> + * offload may clear CWR and corrupt ACE signal (CWR is part of it).
> + * Instead, SKB_GSO_TCP_ACCECN shall be used to avoid CWR corruption.
> + */
I still can't wrap my head around this TBH.
SKB_GSO_TCP_ECN means RFC3168
SKB_GSO_TCP_ACCECN means AccECN
If the HW can correctly detect cwr on first frame and then no cwr
and report that as ECN/RFC3168 - what's the problem? TSO will produce
the exact expected segment sequence.
Is the program that if we re-GRO that frame in SW we end up with
ECN+ACCECN on the same skb?
next prev parent reply other threads:[~2026-08-12 0:30 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-04 21:35 [PATCH v5 net-next 0/2] ECN offload handling series chia-yu.chang
2026-08-04 21:35 ` [PATCH v5 net-next 1/2] net: update comments for SKB_GSO_TCP_ECN and SKB_GSO_TCP_ACCECN chia-yu.chang
2026-08-12 0:30 ` Jakub Kicinski [this message]
2026-08-12 10:33 ` Chia-Yu Chang (Nokia)
2026-08-12 22:54 ` Jakub Kicinski
2026-08-04 21:35 ` [PATCH v5 net-next 2/2] net: hns3: fix GSO_ECN flag setting in the RX path chia-yu.chang
2026-08-06 11:47 ` Jijie Shao
2026-08-11 13:31 ` Jijie Shao
2026-08-12 10:35 ` Chia-Yu Chang (Nokia)
2026-08-12 22:59 ` Jakub Kicinski
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