From mboxrd@z Thu Jan 1 00:00:00 1970 From: Adrien Mazarguil Subject: Re: about rx checksum flags Date: Tue, 31 May 2016 12:08:51 +0200 Message-ID: <20160531100851.GK1428@6wind.com> References: <574C5B9D.4080006@6wind.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Olivier Matz , "dev@dpdk.org" , "Ananyev, Konstantin" , Yuanhan Liu , "Richardson, Bruce" To: "Tan, Jianfeng" Return-path: Received: from mail-wm0-f53.google.com (mail-wm0-f53.google.com [74.125.82.53]) by dpdk.org (Postfix) with ESMTP id 3EB5C2C34 for ; Tue, 31 May 2016 12:08:55 +0200 (CEST) Received: by mail-wm0-f53.google.com with SMTP id n129so122952967wmn.1 for ; Tue, 31 May 2016 03:08:55 -0700 (PDT) Content-Disposition: inline In-Reply-To: List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Tue, May 31, 2016 at 10:43:29AM +0800, Tan, Jianfeng wrote: > Hi Oliver, > > > On 5/30/2016 11:26 PM, Olivier Matz wrote: > >Hi, > > > >I'm planning to add the support for offloads in virtio-net pmd. > >It appears that the current rx flags in mbuf are not sufficient to > >describe the state of a packet received from a virtual driver. > >I think we need a way to say "the checksum in the packet data is > >not calculated, but the integrity of the data is verified". > > I also met this problem :-). Glad to see you raise it up in the mail list. > > > > >Currently, we have one flag for L4 (same for IP): > > > > PKT_RX_L4_CKSUM_BAD: L4 cksum of RX pkt. is not OK. > > > >This has also another problem that has already been discussed [1]: > >if no flag is set, it is expected that the checksum is verified by > >hw, but there is no way to say "the hw does not know if the cksum > >is correct". > > > >I would like to extend this flag to a 4-state value (2 bits): > > > > PKT_RX_L4_CKSUM_UNKNOWN: no information about the RX L4 checksum > > -> the application should verify the checksum by sw > > > > PKT_RX_L4_CKSUM_BAD: the L4 checksum in the packet is wrong > > -> the application can drop the packet without additional check > > > > PKT_RX_L4_CKSUM_GOOD: the L4 checksum in the packet is valid > > -> the application can accept the packet without verifying the > > checksum by sw > > > > PKT_RX_L4_CKSUM_NONE: the L4 checksum is not correct in the packet > > data, but the integrity of the L4 header is verified. > > -> the application can process the packet but must not verify the > > checksum by sw. It has to take care to recalculate the cksum > > if the packet is transmitted (either by sw or using tx offload) > > > >To keep the compatibility with application, the old flag is kept at the > >same value, and a new flag is added. It is assumed that the behavior > >of applications was: > > > > PKT_RX_L4_CKSUM_BAD = 0 -> packet is accepted > > PKT_RX_L4_CKSUM_BAD = 1 -> packet is dropped > > > >The new checksum states for L4 (same for IP) would be: > > > > old flag new flag meaning > > 0 0 PKT_RX_L4_CKSUM_UNKNOWN > > 1 0 PKT_RX_L4_CKSUM_BAD > > 0 1 PKT_RX_L4_CKSUM_GOOD > > 1 1 PKT_RX_L4_CKSUM_NONE > > > >With this, an old application that only checks the old flag, and > >running using a dpdk having this modification would accept GOOD and > >UNKNOWN packets (like today), drop BAD packets (like today) and > >drop NONE packets (this is a new feature that has to be explicitly > >enabled by the application). > > > > > >Any comment? > > Why not take care of PKT_RX_IP_CKSUM_BAD? Is it too easy for sw to handle? I thought PKT_RX_IP_CKSUM_BAD was to be modified in a similar fashion, but since you raise the issue, mlx4/mlx5 need this as well. These boards only report "good" checksums for L3 and L4. > For virtio, there's only one bit, VIRTIO_NET_HDR_F_DATA_VALID, to indicate > that checksum is valid. Shall we differentiate L3 checksum and L4 checksum > in rte_mbuf.ol_flags? > > Thanks, > Jianfeng > > > > >Olivier > > > > > >[1] http://dpdk.org/ml/archives/dev/2015-January/011550.html > -- Adrien Mazarguil 6WIND