From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Pismenny Subject: Re: [net-next 01/12] net/mlx5e: Add UDP GSO support Date: Mon, 2 Jul 2018 22:17:04 +0300 Message-ID: References: <20180628215103.9141-1-saeedm@mellanox.com> <20180628215103.9141-2-saeedm@mellanox.com> <7f108395-5782-eb4c-1023-5c513bd13079@mellanox.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: David Miller , Network Development , Saeed Mahameed , ogerlitz@mellanox.com, yossiku@mellanox.com To: Alexander Duyck , Willem de Bruijn Return-path: Received: from mail-eopbgr60081.outbound.protection.outlook.com ([40.107.6.81]:10930 "EHLO EUR04-DB3-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752167AbeGBTRV (ORCPT ); Mon, 2 Jul 2018 15:17:21 -0400 In-Reply-To: Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 7/2/2018 6:32 PM, Alexander Duyck wrote: > > > On Mon, Jul 2, 2018 at 7:46 AM Willem de Bruijn > > wrote: > > On Mon, Jul 2, 2018 at 9:34 AM Willem de Bruijn > > wrote: > > > > On Mon, Jul 2, 2018 at 1:30 AM Boris Pismenny > > wrote: > > > > > > > > > > > > On 7/2/2018 4:45 AM, Willem de Bruijn wrote: > > > >>> I've noticed that we could get cleaner code in our driver > if we remove > > > >>> these two lines from net/ipv4/udp_offload.c: > > > >>> if (skb_is_gso(segs)) > > > >>>                mss *= skb_shinfo(segs)->gso_segs; > > > >>> > > > >>> I think that this is correct in case of GSO_PARTIAL > segmentation for the > > > >>> following reasons: > > > >>> 1. After this change the UDP payload field is consistent > with the IP > > > >>> header payload length field. Currently, IPv4 length is 1500 > and UDP > > > >>> total length is the full unsegmented length. > > > > > > > > How does this simplify the driver? Does it currently have to > > > > change the udph->length field to the mss on the wire, because the > > > > device only splits + replicates the headers + computes the csum? > > > > > > Yes, this is the code I have at the moment. > > > > > > The device's limitation is more subtle than this. It could > adjust the > > > length, but then the checksum would be wrong. > > > > I see. We do have to keep in mind other devices. Alexander's ixgbe > > RFC patch does not have this logic, so that device must update the > > field directly. > > > > https://patchwork.ozlabs.org/patch/908396/ > > To be clear, I think it's fine to remove these two lines if it does > not cause > problems for the ixgbe. It's quite possible that that device sets > the udp > length field unconditionally, ignoring the previous value. In which > case both > devices will work after this change without additional driver logic. > > > I would prefer we didn’t modify this. Otherwise we cannot cancel out the > length from the partial checksum when the time comes. The ixgbe code was > making use of it if I recall. > AFAIU, the ixgbe patch doesn't use this. Instead the length is obtained by the following code for both TCP and UDP segmentation: paylen = skb->len - l4_offset; Could you please check to see if this is actually required?