From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E9E91ECAAD3 for ; Fri, 9 Sep 2022 12:44:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231488AbiIIMow (ORCPT ); Fri, 9 Sep 2022 08:44:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54324 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231252AbiIIMov (ORCPT ); Fri, 9 Sep 2022 08:44:51 -0400 Received: from mail-pf1-x42e.google.com (mail-pf1-x42e.google.com [IPv6:2607:f8b0:4864:20::42e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EA73F2B188; Fri, 9 Sep 2022 05:44:48 -0700 (PDT) Received: by mail-pf1-x42e.google.com with SMTP id d82so1545782pfd.10; Fri, 09 Sep 2022 05:44:48 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date; bh=VhZla9GFvX7C+5pJWeSUEDxGd4lVsApmfsr27FzTwyY=; b=EuLEo9EMaoB2IZaEKQSlXqdfMBKpBB3M+flHICO4O6pLeMy8EEIn7B9jCzqzglnYIu ppH17NbpqEsd49rVXV8PEK+NMm4VYN/g2FXv2j4k+me4ZOsH49HjsElQaWuWeA8/7TDY idVX5oahjgzUu4q9QjAVKr4K3di793PxJa6c5XIfSgULxjkxN2f3zlxgsA2peVlTaMDB LvfG+WUPU6e8KDjwel3mXCFRF6H5guC9ZsUZKc587EtNgk9lXt8yS4swdKafo951PaVX 1XQKeGqR6BnZ8bW7ceKIZ67lVtQnmQkqD9GwHeOI6BV2OAvLTonsb3CitVU+bATDJ0IW ErtA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date; bh=VhZla9GFvX7C+5pJWeSUEDxGd4lVsApmfsr27FzTwyY=; b=Ot5zJuAwLawWRjhusSOFdu8pDUCEFU0kxO2Lw9Z2F3Wicx+aYCXumCrvtlFm2JRUvO gH+LasyUHrmCdH1BQQb7AsGzg2JYf4yohlvHnfJ8+f7eOsY3SKy7qLDUqFFprj5Nm1rc WL/xMpWUnZtXawT06gdXgW1fNdQtVCVm4joAHEV1fqgAdGvtJwN4gX8pvrx4BLnemlnL Ks7LHDlpjmGb6eKcPFAgmDirElUvrpLOc7r5dTD73pTjEmCiBFtFZ9q1NsuBsCCy76kh ZL9xAGNM3rOifAxTPbJnhaFXnXokfra2byraeco/cky/MlPf6u/4o8ITQb9lPjzjrLeX XcFw== X-Gm-Message-State: ACgBeo0LJ6xGBqXYGOOgrBxHe2rmlwZ7gQYnVM5LPNYcLjsLcQfbqvvB gztEs4sMUk0KAvwaGhCxIGbxtKlxt8pPxSsXuz0= X-Google-Smtp-Source: AA6agR4czFXLfB5kg0j2ww0+x9ZnPVCyIqwzSXb55TDv+81vTM5U8TxLluZCf0VWG0xet2csgMMb15eDppj8cA+KqEw= X-Received: by 2002:a05:6a00:1995:b0:52d:5c39:3f61 with SMTP id d21-20020a056a00199500b0052d5c393f61mr14026007pfl.83.1662727488296; Fri, 09 Sep 2022 05:44:48 -0700 (PDT) MIME-Version: 1.0 References: <166256538687.1434226.15760041133601409770.stgit@firesoul> <166256558657.1434226.7390735974413846384.stgit@firesoul> <9aab9ef1-446d-57ab-5789-afffe27801f4@redhat.com> <593cc1df-8b65-ae9e-37eb-091b19c4d00e@redhat.com> <51f40ca1-ccf2-bcc3-d20d-931ad0d22526@redhat.com> In-Reply-To: <51f40ca1-ccf2-bcc3-d20d-931ad0d22526@redhat.com> From: Magnus Karlsson Date: Fri, 9 Sep 2022 14:44:37 +0200 Message-ID: Subject: Re: [xdp-hints] Re: [PATCH RFCv2 bpf-next 17/18] xsk: AF_XDP xdp-hints support in desc options To: Jesper Dangaard Brouer Cc: brouer@redhat.com, Maryam Tahhan , bpf@vger.kernel.org, netdev@vger.kernel.org, xdp-hints@xdp-project.net, larysa.zaremba@intel.com, memxor@gmail.com, Lorenzo Bianconi , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , dave@dtucker.co.uk, Magnus Karlsson , bjorn@kernel.org, Alexander Lobakin Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, Sep 9, 2022 at 2:35 PM Jesper Dangaard Brouer wrote: > > > > On 09/09/2022 12.14, Magnus Karlsson wrote: > > On Fri, Sep 9, 2022 at 11:42 AM Jesper Dangaard Brouer > > wrote: > >> > >> > >> On 09/09/2022 10.12, Maryam Tahhan wrote: > >>> > >>>>>>> > >>>>>>> * Instead encode this information into each metadata entry in the > >>>>>>> metadata area, in some way so that a flags field is not needed (-1 > >>>>>>> signifies not valid, or whatever happens to make sense). This has the > >>>>>>> drawback that the user might have to look at a large number of entries > >>>>>>> just to find out there is nothing valid to read. To alleviate this, it > >>>>>>> could be combined with the next suggestion. > >>>>>>> > >>>>>>> * Dedicate one bit in the options field to indicate that there is at > >>>>>>> least one valid metadata entry in the metadata area. This could be > >>>>>>> combined with the two approaches above. However, depending on what > >>>>>>> metadata you have enabled, this bit might be pointless. If some > >>>>>>> metadata is always valid, then it serves no purpose. But it might if > >>>>>>> all enabled metadata is rarely valid, e.g., if you get an Rx timestamp > >>>>>>> on one packet out of one thousand. > >>>>>>> > >>>>> > >>>>> I like this option better! Except that I have hoped to get 2 bits ;-) > >>>> > >>>> I will give you two if you need it Jesper, no problem :-). > >>>> > >>> > >>> Ok I will look at implementing and testing this and post an update. > >> > >> Perfect if you Maryam have cycles to work on this. > >> > >> Let me explain what I wanted the 2nd bit for. I simply wanted to also > >> transfer the XDP_FLAGS_HINTS_COMPAT_COMMON flag. One could argue that > >> is it redundant information as userspace AF_XDP will have to BTF decode > >> all the know XDP-hints. Thus, it could know if a BTF type ID is > >> compatible with the common struct. This problem is performance as my > >> userspace AF_XDP code will have to do more code (switch/jump-table or > >> table lookup) to map IDs to common compat (to e.g. extract the RX-csum > >> indication). Getting this extra "common-compat" bit is actually a > >> micro-optimization. It is up to AF_XDP maintainers if they can spare > >> this bit. > >> > >> > >>> Thanks folks > >>> > >>>>> The performance advantage is that the AF_XDP descriptor bits will > >>>>> already be cache-hot, and if it indicates no-metadata-hints the AF_XDP > >>>>> application can avoid reading the metadata cache-line :-). > >>>> > >>>> Agreed. I prefer if we can keep it simple and fast like this. > >>>> > >> > >> Great, lets proceed this way then. > >> > >>> > >>> > >> > >> Thinking ahead: We will likely need 3 bits. > >> > >> The idea is that for TX-side, we set a bit indicating that AF_XDP have > >> provided a valid XDP-hints layout (incl corresponding BTF ID). (I would > >> overload and reuse "common-compat" bit if TX gets a common struct). > > > > I think we should reuse the "Rx metadata valid" flag for this since > > this will not be used in the Tx case by definition. In the Tx case, > > this bit would instead mean that the user has provided a valid > > XDP-hints layout. It has a nice symmetry, on Rx it is set by the > > kernel when it has put something relevant in the metadata area. On Tx, > > it is set by user-space if it has put something relevant in the > > metadata area. > > I generally like reusing the bit, *BUT* there is the problem of > (existing) applications ignoring the desc-options bit and forwarding > packets. This would cause the "Rx metadata valid" flag to be seen as > userspace having set the "TX-hints-bit" and kernel would use what is > provided in metadata area (leftovers from RX-hints). IMHO that will be > hard to debug for end-users and likely break existing applications. Good point. I buy this. We need separate Rx and Tx bits. > > We can also reuse this bit when we get a notification > > in the completion queue to indicate if the kernel has produced some > > metadata on tx completions. This could be a Tx timestamp for example. > > > > Big YES, reuse "Rx metadata valid" bit when we get a TX notification in > completion queue. This will be okay because it cannot be forgotten and > misinterpreted as the kernel will have responsibility to update this bit. > > > So hopefully we could live with only two bits :-). > > > > I still think we need three bits ;-) > That should be enough to cover the 6 states: > - RX hints > - RX hints and compat > - TX hints > - TX hints and compat > - TX completion > - TX completion and compat > > > >> But lets land RX-side first, but make sure we can easily extend for the > >> TX-side. >