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 X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 78071C433ED for ; Wed, 7 Apr 2021 18:10:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 49EF561369 for ; Wed, 7 Apr 2021 18:10:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348315AbhDGSKQ (ORCPT ); Wed, 7 Apr 2021 14:10:16 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:54279 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229876AbhDGSKN (ORCPT ); Wed, 7 Apr 2021 14:10:13 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1617819003; 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=sIJdtqncyoAj6XEcbUfmwwq7YASSmOYsJ3oO6UTSf9Q=; b=h94phMiiYSNVKH825FyOFPp4vT4LGCKmRkfCckvthgqp8DmmoqsrYNDgAdr+7GN9TpJ/oN rp7kMJqgF3Bbu2kK83WtYriEgSGFuY++g2yit63rdY2MrIXpBg2GOOMgY/Aotl3J337zht KEr63TRVWP9HRX5wfk99syHWrsmwaLA= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-344--5n6HxgIOiumPSSI8fN5xw-1; Wed, 07 Apr 2021 14:10:02 -0400 X-MC-Unique: -5n6HxgIOiumPSSI8fN5xw-1 Received: by mail-wr1-f71.google.com with SMTP id z7so4004434wrs.17 for ; Wed, 07 Apr 2021 11:10:02 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=sIJdtqncyoAj6XEcbUfmwwq7YASSmOYsJ3oO6UTSf9Q=; b=spLDNCsYCmFuVrSiR0DcgXcUfHtXucErzWryb4d8igEeUTWqimLCmO+my30K3xB/O4 9ZLokT7nZ48RxlaKaZp8qzs3GZM8DKn8iMAniEn/rAoyMArLEPyJv4FNBNdVRHU3M5zS RBsHA1XuYU0i1HE5LyC61ZwnosPejtirqilEdwp3BvJ987OWIYhqiWlfvD7kqRboP5nM OW2O3F28XLffiOU1zvM0cKL8LwjWsTUhT0nEe+RtYMYaWcuOwocQ+0tLfUyrZk6CDa+7 eF/to/8JtGcSWiZ3vIENM1ldVDdRQH1cct7TzkKRc9HdeArf7SHNx/17d/jc1K3h/0y5 kLeQ== X-Gm-Message-State: AOAM530n+knlpiZ1ujzOJ7QUdlvbCN5XGhlSOSRtKU5sz6x9q1UwRiil I9qCbHqj1rjGIWQUJ71W5unjKa08D/pt4fiwcDag2OA8j3w7yff7lefR1iVUOa4dP1gixlhybg1 WNpmcG87fMEzW1p3Y X-Received: by 2002:a05:6000:cd:: with SMTP id q13mr5880700wrx.346.1617818999734; Wed, 07 Apr 2021 11:09:59 -0700 (PDT) X-Google-Smtp-Source: ABdhPJxmGWcbswH2Snjx8UwjwZags/B+Rm4ezDOG1zQdILuxIjW6cC2J/oKr2mnShnnrqIUdzuYpWw== X-Received: by 2002:a05:6000:cd:: with SMTP id q13mr5880682wrx.346.1617818999543; Wed, 07 Apr 2021 11:09:59 -0700 (PDT) Received: from redhat.com ([2a10:800e:f0d3:0:b69b:9fb8:3947:5636]) by smtp.gmail.com with ESMTPSA id c16sm6422763wrx.46.2021.04.07.11.09.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Apr 2021 11:09:59 -0700 (PDT) Date: Wed, 7 Apr 2021 14:09:56 -0400 From: "Michael S. Tsirkin" To: Eric Dumazet Cc: "David S . Miller" , Jakub Kicinski , netdev , Eric Dumazet , Xuan Zhuo , Jason Wang , virtualization@lists.linux-foundation.org Subject: Re: [PATCH net] virtio_net: Do not pull payload in skb->head Message-ID: <20210407140333-mutt-send-email-mst@kernel.org> References: <20210402132602.3659282-1-eric.dumazet@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210402132602.3659282-1-eric.dumazet@gmail.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Apr 02, 2021 at 06:26:02AM -0700, Eric Dumazet wrote: > From: Eric Dumazet > > Xuan Zhuo reported that commit 3226b158e67c ("net: avoid 32 x truesize > under-estimation for tiny skbs") brought a ~10% performance drop. > > The reason for the performance drop was that GRO was forced > to chain sk_buff (using skb_shinfo(skb)->frag_list), which > uses more memory but also cause packet consumers to go over > a lot of overhead handling all the tiny skbs. > > It turns out that virtio_net page_to_skb() has a wrong strategy : > It allocates skbs with GOOD_COPY_LEN (128) bytes in skb->head, then > copies 128 bytes from the page, before feeding the packet to GRO stack. > > This was suboptimal before commit 3226b158e67c ("net: avoid 32 x truesize > under-estimation for tiny skbs") because GRO was using 2 frags per MSS, > meaning we were not packing MSS with 100% efficiency. > > Fix is to pull only the ethernet header in page_to_skb() > > Then, we change virtio_net_hdr_to_skb() to pull the missing > headers, instead of assuming they were already pulled by callers. > > This fixes the performance regression, but could also allow virtio_net > to accept packets with more than 128bytes of headers. > > Many thanks to Xuan Zhuo for his report, and his tests/help. > > Fixes: 3226b158e67c ("net: avoid 32 x truesize under-estimation for tiny skbs") > Reported-by: Xuan Zhuo > Link: https://www.spinics.net/lists/netdev/msg731397.html > Co-Developed-by: Xuan Zhuo > Signed-off-by: Xuan Zhuo > Signed-off-by: Eric Dumazet > Cc: "Michael S. Tsirkin" > Cc: Jason Wang > Cc: virtualization@lists.linux-foundation.org Acked-by: Michael S. Tsirkin Thanks a lot for looking into this, Eric and Xuan Zhuo ! > --- > drivers/net/virtio_net.c | 10 +++++++--- > include/linux/virtio_net.h | 14 +++++++++----- > 2 files changed, 16 insertions(+), 8 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 82e520d2cb1229a0c7b9fd0def3e4a7135536478..0824e6999e49957f7aaf7c990f6259792d42f32b 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -406,9 +406,13 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi, > offset += hdr_padded_len; > p += hdr_padded_len; > > - copy = len; > - if (copy > skb_tailroom(skb)) > - copy = skb_tailroom(skb); > + /* Copy all frame if it fits skb->head, otherwise > + * we let virtio_net_hdr_to_skb() and GRO pull headers as needed. > + */ > + if (len <= skb_tailroom(skb)) > + copy = len; > + else > + copy = ETH_HLEN + metasize; > skb_put_data(skb, p, copy); > > if (metasize) { > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h > index 98775d7fa69632e2c2da30b581a666f7fbb94b64..b465f8f3e554f27ced45c35f54f113cf6dce1f07 100644 > --- a/include/linux/virtio_net.h > +++ b/include/linux/virtio_net.h > @@ -65,14 +65,18 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, > skb_reset_mac_header(skb); > > if (hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) { > - u16 start = __virtio16_to_cpu(little_endian, hdr->csum_start); > - u16 off = __virtio16_to_cpu(little_endian, hdr->csum_offset); > + u32 start = __virtio16_to_cpu(little_endian, hdr->csum_start); > + u32 off = __virtio16_to_cpu(little_endian, hdr->csum_offset); > + u32 needed = start + max_t(u32, thlen, off + sizeof(__sum16)); > + > + if (!pskb_may_pull(skb, needed)) > + return -EINVAL; > > if (!skb_partial_csum_set(skb, start, off)) > return -EINVAL; > > p_off = skb_transport_offset(skb) + thlen; > - if (p_off > skb_headlen(skb)) > + if (!pskb_may_pull(skb, p_off)) > return -EINVAL; > } else { > /* gso packets without NEEDS_CSUM do not set transport_offset. > @@ -102,14 +106,14 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, > } > > p_off = keys.control.thoff + thlen; > - if (p_off > skb_headlen(skb) || > + if (!pskb_may_pull(skb, p_off) || > keys.basic.ip_proto != ip_proto) > return -EINVAL; > > skb_set_transport_header(skb, keys.control.thoff); > } else if (gso_type) { > p_off = thlen; > - if (p_off > skb_headlen(skb)) > + if (!pskb_may_pull(skb, p_off)) > return -EINVAL; > } > } > -- > 2.31.0.208.g409f899ff0-goog