From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: virtio-comment-return-1089-cohuck=redhat.com@lists.oasis-open.org Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: Received: from lists.oasis-open.org (oasis-open.org [10.110.1.242]) by lists.oasis-open.org (Postfix) with ESMTP id 003FA985F62 for ; Thu, 20 Feb 2020 20:25:01 +0000 (UTC) Date: Thu, 20 Feb 2020 15:24:51 -0500 From: "Michael S. Tsirkin" Message-ID: <20200220052144-mutt-send-email-mst@kernel.org> References: MIME-Version: 1.0 In-Reply-To: Subject: Re: [virtio-comment] [PATCH] virtio-net: Add support for correct hdr_len field. Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline To: Vitaly Mireyno Cc: "virtio-comment@lists.oasis-open.org" , "jasowang@redhat.com" List-ID: On Thu, Feb 20, 2020 at 10:18:32AM +0000, Vitaly Mireyno wrote: >=20 > >-----Original Message----- > >From: Michael S. Tsirkin > >Sent: Thursday, 20 February, 2020 12:01 > >To: Vitaly Mireyno > >Cc: virtio-comment@lists.oasis-open.org; jasowang@redhat.com > >Subject: [EXT] Re: [virtio-comment] [PATCH] virtio-net: Add support for = correct hdr_len field. > > > >---------------------------------------------------------------------- > >On Thu, Feb 20, 2020 at 09:51:17AM +0000, Vitaly Mireyno wrote: > >> > >> >-----Original Message----- > >> >From: virtio-comment@lists.oasis-open.org > >> > On Behalf Of Michael S. Tsirkin > >> >Sent: Thursday, 20 February, 2020 10:12 > >> >To: Vitaly Mireyno > >> >Cc: virtio-comment@lists.oasis-open.org; jasowang@redhat.com > >> >Subject: Re: [virtio-comment] [PATCH] virtio-net: Add support for cor= rect hdr_len field. > >> > > >> >--------------------------------------------------------------------- > >> >- On Thu, Oct 24, 2019 at 03:24:43PM +0000, Vitaly Mireyno wrote: > >> >> Some devices benefit from the knowledge of the exact header length = for TSO processing. > >> >> Add a feature bit for a driver that is capable of providing the cor= rect header length for TSO > >packets. > >> >> > >> >> Signed-off-by: Vitaly Mireyno > >> > > >> >So I looked at implementing this and maybe this was not such a good i= dea after all. > >> > > >> >How would we implement this in Linux? > >> >Current code just puts skb_headlen there which is # of bytes in the l= inear buffer. > >> >Which I guess it often the header, but not at all always. > >> > > >> >Should this have been limited to TSO packets? > >> > > >> >I also could not figure out how this is useful for the host. > >> >Could you enlighten me pls? > >> > >> As see it, header length is essential for TSO, and maybe not so useful= for non-TSO. > > > >So maybe we should limit this for when gso type is actually set? >=20 > Do you mean the hdr_len field will be valid only for TSO packets, or it w= ill be accurate only for TSO packets? > I'm fine with both options. Let's say accurate only for TSO. Can you write a spec patch like this? > > > >> To calculate the header length, I suppose a Linux driver could do some= thing like: > >> skb_transport_header(skb) + tcp_hdrlen(skb) - skb->data That's only good for TCP though. > > > >That's parsing the header in software. Why not have the card do it in ha= rdware? > > >=20 > It depends on hw architecture. The architecture I'm familiar with, the hw= can parse the header, but it happens too late for the segmentation decisio= n. >=20 >=20 > >-- > >MST This publicly archived list offers a means to provide input to the=0D OASIS Virtual I/O Device (VIRTIO) TC.=0D =0D In order to verify user consent to the Feedback License terms and=0D to minimize spam in the list archive, subscription is required=0D before posting.=0D =0D Subscribe: virtio-comment-subscribe@lists.oasis-open.org=0D Unsubscribe: virtio-comment-unsubscribe@lists.oasis-open.org=0D List help: virtio-comment-help@lists.oasis-open.org=0D List archive: https://lists.oasis-open.org/archives/virtio-comment/=0D Feedback License: https://www.oasis-open.org/who/ipr/feedback_license.pdf= =0D List Guidelines: https://www.oasis-open.org/policies-guidelines/mailing-lis= ts=0D Committee: https://www.oasis-open.org/committees/virtio/=0D Join OASIS: https://www.oasis-open.org/join/