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 autolearn=unavailable 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 E6E2DC001E3 for ; Mon, 12 Apr 2021 09:18:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B57D061209 for ; Mon, 12 Apr 2021 09:18:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238347AbhDLJSG (ORCPT ); Mon, 12 Apr 2021 05:18:06 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:21993 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239298AbhDLJMz (ORCPT ); Mon, 12 Apr 2021 05:12:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618218750; 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=9MX/q65ulilBbiEmH9SpX/hWPbm4em/YWE26ePKzMIY=; b=hxegpaqbRqTCbX4NxRDHe97SA+3DcrN8SBmPYACarJZcBfEHlBhDiO7glZ2x+z4pkJUGf3 dUPOI3n6d0szOhYQrfyvI2k51eaDx4RGdoOFBfm2E/a8CgwrLw35us5blhGv4VOV5hZsoQ 6Y3QWrTd6p35JVdYGAyW0M0cKHe+4N4= Received: from mail-wr1-f72.google.com (mail-wr1-f72.google.com [209.85.221.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-297-U9iTrLTGOK6CUjmw91qwtg-1; Mon, 12 Apr 2021 05:12:28 -0400 X-MC-Unique: U9iTrLTGOK6CUjmw91qwtg-1 Received: by mail-wr1-f72.google.com with SMTP id v3so779598wrr.22 for ; Mon, 12 Apr 2021 02:12:28 -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=9MX/q65ulilBbiEmH9SpX/hWPbm4em/YWE26ePKzMIY=; b=LU70QCmDXPWQSG/epA3g1QZkmS6Psbz4gYiNPXZuRHsceGzNuuKqzLI/qr8gHWCGA4 Gnu+ksC2MI/N17cw9j30VPEWB5IToazF2yVASGQvKWclmDp/pMdWEHxGgVgZn5GGrGng kzL/N/j5cFaIJFCyQp8Q3SDRIOXf4trdBLhI83h913YMxvj01ynV5qgSCJUuvibOFsDZ linK+xvjGdA/sH+iO1v+KhetlreXkL1PDnAwrfq3t/vos9qbpRbQ2noQTZMovrVU2mTw iXMA1yihTuYz8lU8vHyWeFbldyA1dmy8Z3W29+0CORWLdUT2O8mCb/rmtscFOxJOkVyp yKEw== X-Gm-Message-State: AOAM533aEL6iKCr7IQg87YaXP7UpHPlAc7yvSHUx0vf/pl1Dt+HSdhhW rSDM5nts6wXH6mxU/Yg2vFE2pWueysFbHztGL2PHQYEruJOf20A130pDvTL7mhbGmgE1jqOgcIc x/lKOpYOFcGnHkY16 X-Received: by 2002:a1c:c355:: with SMTP id t82mr8739027wmf.160.1618218747305; Mon, 12 Apr 2021 02:12:27 -0700 (PDT) X-Google-Smtp-Source: ABdhPJytReoQtggqwIdF15Nw8+1JD7ZnJzHU1656q8IXOGUyc29YkyAmvn7gN5OjoJW6bjg/x6usvw== X-Received: by 2002:a1c:c355:: with SMTP id t82mr8739013wmf.160.1618218747161; Mon, 12 Apr 2021 02:12:27 -0700 (PDT) Received: from redhat.com ([2a10:8006:2281:0:1994:c627:9eac:1825]) by smtp.gmail.com with ESMTPSA id 24sm13711646wmg.19.2021.04.12.02.12.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Apr 2021 02:12:26 -0700 (PDT) Date: Mon, 12 Apr 2021 05:12:23 -0400 From: "Michael S. Tsirkin" To: Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Xuan Zhuo , Eric Dumazet , Jason Wang , virtualization@lists.linux-foundation.org, "David S. Miller" , Sasha Levin Subject: Re: [PATCH 4.19 28/66] virtio_net: Do not pull payload in skb->head Message-ID: <20210412051204-mutt-send-email-mst@kernel.org> References: <20210412083958.129944265@linuxfoundation.org> <20210412083959.037627043@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210412083959.037627043@linuxfoundation.org> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Apr 12, 2021 at 10:40:34AM +0200, Greg Kroah-Hartman wrote: > From: Eric Dumazet > > [ Upstream commit 0f6925b3e8da0dbbb52447ca8a8b42b371aac7db ] > > 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 > Signed-off-by: David S. Miller > Signed-off-by: Sasha Levin Note that an issue related to this patch was recently reported. It's quite possible that the root cause is a bug elsewhere in the kernel, but it probably makes sense to defer the backport until we know more ... > --- > 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 0b1c6a8906b9..06ddf009f833 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -413,9 +413,13 @@ 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 a1829139ff4a..8f48264f5dab 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; > } > } > -- > 2.30.2 > >