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=-17.3 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,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_RED,USER_AGENT_SANE_1 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 797F5C433ED for ; Tue, 6 Apr 2021 02:03:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2D30B61002 for ; Tue, 6 Apr 2021 02:03:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239520AbhDFCDo (ORCPT ); Mon, 5 Apr 2021 22:03:44 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:29508 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238649AbhDFCDn (ORCPT ); Mon, 5 Apr 2021 22:03:43 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1617674616; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=NE0jWj+e38GjOmQ3dzCrwVMGgnT57rdacD0LpLJtGWM=; b=O9il0AjiCWAEBMB7fcPnLlgm8LINK1/10EW7gr0JSQ3z6dEf1uTe1c0QONrpwhvLtIgEBd 7hHbDJ+YxIfrdJi8D0jXbuPam3iPO7cCTT3h5RSXIvpL8njtbFBQuryTRxevjbYTSNl1Ge c6Sf4kFQ/0n36OvYS2JuAasmO9AJgmA= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-271--1dPHH2oMvmRLN28cKfmKw-1; Mon, 05 Apr 2021 22:03:32 -0400 X-MC-Unique: -1dPHH2oMvmRLN28cKfmKw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id AC20287A82A; Tue, 6 Apr 2021 02:03:30 +0000 (UTC) Received: from wangxiaodeMacBook-Air.local (ovpn-13-96.pek2.redhat.com [10.72.13.96]) by smtp.corp.redhat.com (Postfix) with ESMTP id 586F21C4; Tue, 6 Apr 2021 02:03:24 +0000 (UTC) Subject: Re: [PATCH net] virtio_net: Do not pull payload in skb->head To: Eric Dumazet , "David S . Miller" , Jakub Kicinski Cc: netdev , Eric Dumazet , Xuan Zhuo , "Michael S. Tsirkin" , virtualization@lists.linux-foundation.org References: <20210402132602.3659282-1-eric.dumazet@gmail.com> From: Jason Wang Message-ID: <61d05135-3a25-b145-769f-ee7c72f46d7b@redhat.com> Date: Tue, 6 Apr 2021 10:03:22 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <20210402132602.3659282-1-eric.dumazet@gmail.com> Content-Type: text/plain; charset=gbk; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org ÔÚ 2021/4/2 ÏÂÎç9:26, Eric Dumazet дµÀ: > 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: Jason Wang > 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; > } > }