From: "Michael S. Tsirkin" <mst@redhat•com>
To: "Chia-Yu Chang (Nokia)" <chia-yu.chang@nokia-bell-labs•com>
Cc: "tariqt@nvidia•com" <tariqt@nvidia•com>,
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Subject: Re: [PATCH v1 net-next 3/3] virtio_net: Accurate ECN flag in virtio_net_hdr
Date: Mon, 2 Feb 2026 12:19:48 -0500 [thread overview]
Message-ID: <20260202121830-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <AM9PR07MB79696F945D8DBEF370CD4DC6A39AA@AM9PR07MB7969.eurprd07.prod.outlook.com>
On Mon, Feb 02, 2026 at 04:56:38PM +0000, Chia-Yu Chang (Nokia) wrote:
> > -----Original Message-----
> > From: Michael S. Tsirkin <mst@redhat•com>
> > Sent: Sunday, February 1, 2026 10:18 AM
> > To: Chia-Yu Chang (Nokia) <chia-yu.chang@nokia-bell-labs•com>
> > Cc: tariqt@nvidia•com; linux-rdma@vger•kernel.org; shaojijie@huawei•com; shenjian15@huawei•com; salil.mehta@huawei•com; mbloch@nvidia•com; saeedm@nvidia•com; leon@kernel•org; eperezma@redhat•com; brett.creeley@amd•com; jasowang@redhat•com; virtualization@lists•linux.dev; xuanzhuo@linux•alibaba.com; pabeni@redhat•com; edumazet@google•com; parav@nvidia•com; linux-doc@vger•kernel.org; corbet@lwn•net; horms@kernel•org; dsahern@kernel•org; kuniyu@google•com; bpf@vger•kernel.org; netdev@vger•kernel.org; dave.taht@gmail•com; jhs@mojatatu•com; kuba@kernel•org; stephen@networkplumber•org; xiyou.wangcong@gmail•com; jiri@resnulli•us; davem@davemloft•net; andrew+netdev@lunn•ch; donald.hunter@gmail•com; ast@fiberby•net; liuhangbin@gmail•com; shuah@kernel•org; linux-kselftest@vger•kernel.org; ij@kernel•org; ncardwell@google•com; Koen De Schepper (Nokia) <koen.de_schepper@nokia-bell-labs•com>; g.white@cablelabs•com; ingemar.s.johansson@ericsson•com; mirja.kuehlewind@ericsson•com; cheshire@apple•com; rs.ietf@gmx•at; Jason_Livingood@comcast•com; vidhi_goel@apple•com
> > Subject: Re: [PATCH v1 net-next 3/3] virtio_net: Accurate ECN flag in virtio_net_hdr
> >
> >
> > CAUTION: This is an external email. Please be very careful when clicking links or opening attachments. See the URL nok.it/ext for additional information.
> >
> >
> >
> > Thanks for the patch! Yet something to improve:
> >
> > On Sat, Jan 31, 2026 at 11:55:10PM +0100, chia-yu.chang@nokia-bell-labs•com wrote:
> > > From: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs•com>
> > >
> > > Unlike RFC 3168 ECN, accurate ECN uses the CWR flag as part of the ACE
> > > field to count new packets with CE mark; however, it will be corrupted
> > > by the RFC 3168 ECN-aware TSO. Therefore, fallback shall be applied by
> > > seting NETIF_F_GSO_ACCECN to ensure that the CWR flag should not be
> > > changed within a super-skb.
> > >
> > > To apply the aforementieond new AccECN GSO for virtio, new featue bits
> > > for host and guest are added for feature negotiation between driver
> > > and device. And the translation of Accurate ECN GSO flag between
> > > virtio_net_hdr and skb header for NETIF_F_GSO_ACCECN is also added to
> > > avoid CWR flag corruption due to RFC3168 ECN TSO.
> > >
> > > Signed-off-by: Chia-Yu Chang <chia-yu.chang@nokia-bell-labs•com>
> >
> >
> > To the best of my understanding, this is a new feature - support for VIRTIO_NET_F_HOST_ACCECN, VIRTIO_NET_F_GUEST_ACCECN?
> > The commit log makes it sound like it fixes some behaviour for existing hardware, but that is not the case.
> >
>
> Thansk for the feedback, I will update commit message in v3.
> >
> > > ---
> > > v2:
> > > - Replace VIRTIO_NET_HDR_GSO_ECN with VIRTIO_NET_HDR_GSO_ECN_FLAGS
> >
> > but where is v2? this is v1...
>
> I shall update this version as v2, will do at the next version.
>
> [...]
> > > diff --git a/include/uapi/linux/virtio_net.h
> > > b/include/uapi/linux/virtio_net.h index 1db45b01532b..af5bfe45aa1f
> > > 100644
> > > --- a/include/uapi/linux/virtio_net.h
> > > +++ b/include/uapi/linux/virtio_net.h
> > > @@ -56,6 +56,8 @@
> > > #define VIRTIO_NET_F_MQ 22 /* Device supports Receive Flow
> > > * Steering */
> > > #define VIRTIO_NET_F_CTRL_MAC_ADDR 23 /* Set MAC address */
> > > +#define VIRTIO_NET_F_HOST_ACCECN 25 /* Host can handle GSO of AccECN
> > > +*/ #define VIRTIO_NET_F_GUEST_ACCECN 26 /* Guest can handle GSO of
> > > +AccECN */
> > > #define VIRTIO_NET_F_DEVICE_STATS 50 /* Device can provide
> > > device-level statistics. */ #define VIRTIO_NET_F_VQ_NOTF_COAL 52 /* Device supports virtqueue notification coalescing */
> > > #define VIRTIO_NET_F_NOTF_COAL 53 /* Device supports notifications coalescing */
> > > @@ -165,6 +167,9 @@ struct virtio_net_hdr_v1 { #define
> > > VIRTIO_NET_HDR_GSO_UDP_TUNNEL (VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV4 | \
> > > VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6)
> > > #define VIRTIO_NET_HDR_GSO_ECN 0x80 /* TCP has ECN set */
> > > +#define VIRTIO_NET_HDR_GSO_ACCECN 0x10 /* TCP AccECN segmentation */
> > > +#define VIRTIO_NET_HDR_GSO_ECN_FLAGS (VIRTIO_NET_HDR_GSO_ECN | \
> > > + VIRTIO_NET_HDR_GSO_ACCECN)
> > > __u8 gso_type;
> > > __virtio16 hdr_len; /* Ethernet + IP + tcp/udp hdrs */
> > > __virtio16 gso_size; /* Bytes to append to hdr_len per frame */
> >
> >
> > UAPI changes need to be added to the virtio spec.
> > Pls get this approved by the virtio TC.
> > Thanks!
>
> There were some discussions last October in virtio-comment@lists•linux.dev mailing list.
That's it I could not find it. Could you include the archive link pls?
> At that moment, it is suggested to make Linux kernel accept new comments for SKB_GSO_TCP_ECN and SKB_GSO_TCP_ACCECN first.
> So, could virtio-spec colleague give your feedback? (Parav?).
>
> Otherwise, the CWR handling of virtio will be wrong after all Accurate ECN commits are merged in Linux.
>
> Chia-Yu
if there's a general agreement we don't need to block linux on tc
approval.
--
MST
next prev parent reply other threads:[~2026-02-02 17:19 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-31 22:55 [PATCH v1 net-next 0/3] ECN offload handling for AccECN series chia-yu.chang
2026-01-31 22:55 ` [PATCH v1 net-next 1/3] net: update commnets for SKB_GSO_TCP_ECN and SKB_GSO_TCP_ACCECN chia-yu.chang
2026-02-01 9:01 ` Michael S. Tsirkin
2026-01-31 22:55 ` [PATCH v1 net-next 2/3] net: hns3/mlx5e: avoid corrupting CWR flag when receiving GRO packet chia-yu.chang
2026-02-01 9:05 ` Michael S. Tsirkin
2026-02-02 16:44 ` Chia-Yu Chang (Nokia)
2026-01-31 22:55 ` [PATCH v1 net-next 3/3] virtio_net: Accurate ECN flag in virtio_net_hdr chia-yu.chang
2026-02-01 9:17 ` Michael S. Tsirkin
2026-02-02 16:56 ` Chia-Yu Chang (Nokia)
2026-02-02 17:19 ` Michael S. Tsirkin [this message]
2026-02-02 21:09 ` Chia-Yu Chang (Nokia)
2026-02-02 23:45 ` Michael S. Tsirkin
2026-02-01 0:45 ` [PATCH v1 net-next 0/3] ECN offload handling for AccECN series Jakub Kicinski
2026-02-02 14:10 ` Chia-Yu Chang (Nokia)
-- strict thread matches above, loose matches on Subject: below --
2026-01-28 14:44 chia-yu.chang
2026-01-28 14:44 ` [PATCH v1 net-next 3/3] virtio_net: Accurate ECN flag in virtio_net_hdr chia-yu.chang
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