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 D0DD2C433F5 for ; Thu, 10 Mar 2022 19:07:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244589AbiCJTHu (ORCPT ); Thu, 10 Mar 2022 14:07:50 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37644 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231898AbiCJTHu (ORCPT ); Thu, 10 Mar 2022 14:07:50 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id DC5B31704EB for ; Thu, 10 Mar 2022 11:06:48 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1646939207; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=gomJ66m2qIlCZfTfMR2uUo9YuZhsZ2IeOLlcOAVHMx8=; b=cuDQWQYfExzQ2aNm8+cNUtvRnDOZAqglK2mPpEo2iTIW2VrfyTJTzlQNkaIjii79yfmAIn s6XVjBxN2wUV5E1ZNUp0NZsEMHT8EyG11BNic2cTHXTG19eX1dOie/z/rKaTUIGf82Fuou SWlCgfB6B9aNTzHuoLv8XQek4M2oNvo= Received: from mail-ej1-f70.google.com (mail-ej1-f70.google.com [209.85.218.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-517-VaZJdg3vPN-EVuPQeSBJBQ-1; Thu, 10 Mar 2022 14:06:47 -0500 X-MC-Unique: VaZJdg3vPN-EVuPQeSBJBQ-1 Received: by mail-ej1-f70.google.com with SMTP id gz16-20020a170907a05000b006db8b2baa10so1212202ejc.1 for ; Thu, 10 Mar 2022 11:06:46 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=gomJ66m2qIlCZfTfMR2uUo9YuZhsZ2IeOLlcOAVHMx8=; b=7AHOH5P3/eRj0uG3PCOq07VKnB+yc2h6NoKuo2FK0XQMxTntu55feXhtWNLt8/gh+M 8BNI7cWIt1szpzWn2YTgDmtGcU1iRYJ7vacpkmbts/42omxIMgzaUHV48yprKArjlXbe QLRtyxG7uY0BerS3mrlO1awhEKVcLORX4jYhUp2iuR7k4x7KTXydD5ZtGi6EcKZwob9v +wXXIejrGo4Q0bC2pZTkac/610ksZDRtxt393qLDxN/hEE/OU+MsGHvtpKtZvs0U8ih0 CGH3pDlD4yl+jxDpY+pe0t1A08FwbFTrJCeK1blBQN+kIABO1V6fuB/EoDwiAXO+NV65 UwVQ== X-Gm-Message-State: AOAM531U9KdUGCu7oZOPzfRt4I/3o1Z40Tm6MEFeqAlUSQd+kmeh22pq //aNsaXD2Sds5mXoLg3VxO/VhVGPVyafWMMJL0kZI9N4YCco4Zr+z5YA7rVxP09iee3TyCmc4Vg 38OWDzYQ4sNld X-Received: by 2002:a17:907:392:b0:6da:8608:e09e with SMTP id ss18-20020a170907039200b006da8608e09emr5532693ejb.89.1646939204175; Thu, 10 Mar 2022 11:06:44 -0800 (PST) X-Google-Smtp-Source: ABdhPJxiaHEhq5PmuQ5pJpUk7YD48G/C26A5LJOE3qDro5wWyMo7FbML/7K1pzZyXja5yksV3kfa9Q== X-Received: by 2002:a17:907:392:b0:6da:8608:e09e with SMTP id ss18-20020a170907039200b006da8608e09emr5532549ejb.89.1646939201654; Thu, 10 Mar 2022 11:06:41 -0800 (PST) Received: from alrua-x1.borgediget.toke.dk ([2a0c:4d80:42:443::2]) by smtp.gmail.com with ESMTPSA id q9-20020a170906770900b006d20acf7e2bsm2100313ejm.200.2022.03.10.11.06.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Mar 2022 11:06:40 -0800 (PST) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 338381A8960; Thu, 10 Mar 2022 20:06:40 +0100 (CET) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Lorenzo Bianconi Cc: Lorenzo Bianconi , bpf@vger.kernel.org, netdev@vger.kernel.org, davem@davemloft.net, kuba@kernel.org, ast@kernel.org, daniel@iogearbox.net, brouer@redhat.com, pabeni@redhat.com, echaudro@redhat.com, toshiaki.makita1@gmail.com, andrii@kernel.org Subject: Re: [PATCH v4 bpf-next 2/3] veth: rework veth_xdp_rcv_skb in order to accept non-linear skb In-Reply-To: References: <24703dbc3477a4b3aaf908f6226a566d27969f83.1646755129.git.lorenzo@kernel.org> <87ee3auk70.fsf@toke.dk> X-Clacks-Overhead: GNU Terry Pratchett Date: Thu, 10 Mar 2022 20:06:40 +0100 Message-ID: <87ilsly6db.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Lorenzo Bianconi writes: >> Lorenzo Bianconi writes: >> >> > Introduce veth_convert_xdp_buff_from_skb routine in order to >> > convert a non-linear skb into a xdp buffer. If the received skb >> > is cloned or shared, veth_convert_xdp_buff_from_skb will copy it >> > in a new skb composed by order-0 pages for the linear and the >> > fragmented area. Moreover veth_convert_xdp_buff_from_skb guarantees >> > we have enough headroom for xdp. >> > This is a preliminary patch to allow attaching xdp programs with frags >> > support on veth devices. >> > >> > Signed-off-by: Lorenzo Bianconi >> >> It's cool that we can do this! A few comments below: > > Hi Toke, > > thx for the review :) > > [...] > >> > +static int veth_convert_xdp_buff_from_skb(struct veth_rq *rq, >> > + struct xdp_buff *xdp, >> > + struct sk_buff **pskb) >> > +{ >> >> nit: It's not really "converting" and skb into an xdp_buff, since the >> xdp_buff lives on the stack; so maybe 'veth_init_xdp_buff_from_skb()'? > > I kept the previous naming convention used for xdp_convert_frame_to_buff() > (my goal would be to move it in xdp.c and reuse this routine for the > generic-xdp use case) but I am fine with > veth_init_xdp_buff_from_skb(). Consistency is probably good, but right now we have functions of the form 'xdp_convert_X_to_Y()' and 'xdp_update_Y_from_X()'. So to follow that you'd have either 'veth_update_xdp_buff_from_skb()' or 'veth_convert_skb_to_xdp_buff()' :) >> > + struct sk_buff *skb = *pskb; >> > + u32 frame_sz; >> > >> > if (skb_shared(skb) || skb_head_is_locked(skb) || >> > - skb_is_nonlinear(skb) || headroom < XDP_PACKET_HEADROOM) { >> > + skb_shinfo(skb)->nr_frags) { >> >> So this always clones the skb if it has frags? Is that really needed? > > if we look at skb_cow_data(), paged area is always considered not writable Ah, right, did not know that. Seems a bit odd, but OK. >> Also, there's a lot of memory allocation and copying going on here; have >> you measured the performance? > > even in the previous implementation we always reallocate the skb if the > conditions above are verified so I do not expect any difference in the single > buffer use-case but I will run some performance tests. No, I wouldn't expect any difference for the single-buffer case, but I would also be interested in how big the overhead is of having to copy the whole jumbo-frame? BTW, just noticed one other change - before we had: > - headroom = skb_headroom(skb) - mac_len; > if (skb_shared(skb) || skb_head_is_locked(skb) || > - skb_is_nonlinear(skb) || headroom < XDP_PACKET_HEADROOM) { And in your patch that becomes: > + } else if (skb_headroom(skb) < XDP_PACKET_HEADROOM && > + pskb_expand_head(skb, VETH_XDP_HEADROOM, 0, GFP_ATOMIC)) { > + goto drop; So the mac_len subtraction disappeared; that seems wrong? >> > + >> > + if (xdp_buff_has_frags(&xdp)) >> > + skb->data_len = skb_shinfo(skb)->xdp_frags_size; >> > + else >> > + skb->data_len = 0; >> >> We can remove entire frags using xdp_adjust_tail, right? Will that get >> propagated in the right way to the skb frags due to the dual use of >> skb_shared_info, or? > > bpf_xdp_frags_shrink_tail() can remove entire frags and it will modify > metadata contained in the skb_shared_info (e.g. nr_frags or the frag > size of the given page). We should consider the data_len field in this > case. Agree? Right, that's what I assumed; makes sense. But adding a comment mentioning this above the update of data_len might be helpful? :) -Toke