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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 0C544C04FCF for ; Mon, 12 Apr 2021 09:11:53 +0000 (UTC) Received: from smtp3.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 7F8646124C for ; Mon, 12 Apr 2021 09:11:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7F8646124C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=virtualization-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by smtp3.osuosl.org (Postfix) with ESMTP id 29A7B6062E; Mon, 12 Apr 2021 09:11:52 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp3.osuosl.org ([127.0.0.1]) by localhost (smtp3.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id h40BTjNUgmGj; Mon, 12 Apr 2021 09:11:51 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [IPv6:2605:bc80:3010:104::8cd3:938]) by smtp3.osuosl.org (Postfix) with ESMTP id A100D605CB; Mon, 12 Apr 2021 09:11:50 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 76925C000C; Mon, 12 Apr 2021 09:11:50 +0000 (UTC) Received: from smtp3.osuosl.org (smtp3.osuosl.org [IPv6:2605:bc80:3010::136]) by lists.linuxfoundation.org (Postfix) with ESMTP id DEA6EC000A for ; Mon, 12 Apr 2021 09:11:49 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by smtp3.osuosl.org (Postfix) with ESMTP id B327F6062E for ; Mon, 12 Apr 2021 09:11:49 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from smtp3.osuosl.org ([127.0.0.1]) by localhost (smtp3.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Bdxtfoj6144l for ; Mon, 12 Apr 2021 09:11:48 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.8.0 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [63.128.21.124]) by smtp3.osuosl.org (Postfix) with ESMTPS id 6C1F1605CB for ; Mon, 12 Apr 2021 09:11:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1618218707; 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=Z4CGSPG8tOPRpMOFt0W6LolJTlNS23GsEDS81NNit60=; b=BEEkikuboSBT2qQO0qrQ71dsjSn0/Fs2yfunnxCR+SxPBQHiHa8AQViQ7SKQZs/EU4dHaq B4DX31DkXMkCGyib41ymVEaJINGcyDYiD9YbJHpMt96sEj51V5csW4fHVKM9XGTM5hHW76 fT5rVjkVgaMYVYWU+2I4jK3RMp2wKvg= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-546-pzAYGkAiMMGtAKmxMpQfKg-1; Mon, 12 Apr 2021 05:11:45 -0400 X-MC-Unique: pzAYGkAiMMGtAKmxMpQfKg-1 Received: by mail-wr1-f70.google.com with SMTP id y4so1408513wrs.7 for ; Mon, 12 Apr 2021 02:11:44 -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=Z4CGSPG8tOPRpMOFt0W6LolJTlNS23GsEDS81NNit60=; b=CSrjIKu5EE7YPGowWvv2MbyTkmx1HMtiIZWSjLRV2T03JAtF7xBTF9i0Dc0KaiUjh2 11YNmDEzTRX1vXPcaxIwC0p+r87giMIJgw0/ZqHJT9c/a5rkNTodZu+Q1WA+WWzKG30j A9a1H3Sr6Ju6VmAdTYh8QPbrxlMcB+8i00Yh5BRzIpCav77SeLsY70b5EbffPW6bh5jb Fok2Rq+yUdEhSCNin/lOlLGhdRcEz6MT2PFVY1ELg1pEKjhdv0F5+8nTLO3LzV4HI594 I0a+zdW16vSB903t3ZOAcDio2Lu/XUgretsYCaQB44sWcjzhNSQtnN6CfxEYa7ZiwfBa bxcQ== X-Gm-Message-State: AOAM533+fjnZOyBM1dYXRBCqdu7PkHv5jc6BSarVR3k0cx4/RYztwzBF whFyVNfbAwHf3lWQ/gamiTP2lHbTwpsqx5UXnozmYHOnl2leMPQogaLLLYf6kwraRwkDTFlSLcw u8HZpjI0mG9t0gyKtOj6zgQdGkxThJifNjex2NobtjA== X-Received: by 2002:a5d:4e4d:: with SMTP id r13mr5212617wrt.132.1618218703976; Mon, 12 Apr 2021 02:11:43 -0700 (PDT) X-Google-Smtp-Source: ABdhPJzbpV1As7D9dyJG1976JRdBrYE4HjVYKZIQxqsW0bAy1gaSfmpLSNvIIk81JI1cpg3MnYPDbw== X-Received: by 2002:a5d:4e4d:: with SMTP id r13mr5212601wrt.132.1618218703837; Mon, 12 Apr 2021 02:11:43 -0700 (PDT) Received: from redhat.com ([2a10:8006:2281:0:1994:c627:9eac:1825]) by smtp.gmail.com with ESMTPSA id q186sm14842311wma.21.2021.04.12.02.11.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Apr 2021 02:11:42 -0700 (PDT) Date: Mon, 12 Apr 2021 05:11:40 -0400 From: "Michael S. Tsirkin" To: Greg Kroah-Hartman Subject: Re: [PATCH 5.10 055/188] virtio_net: Do not pull payload in skb->head Message-ID: <20210412051010-mutt-send-email-mst@kernel.org> References: <20210412084013.643370347@linuxfoundation.org> <20210412084015.479443671@linuxfoundation.org> MIME-Version: 1.0 In-Reply-To: <20210412084015.479443671@linuxfoundation.org> Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Cc: Xuan Zhuo , linux-kernel@vger.kernel.org, stable@vger.kernel.org, virtualization@lists.linux-foundation.org, Eric Dumazet , "David S. Miller" X-BeenThere: virtualization@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Linux virtualization List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Mon, Apr 12, 2021 at 10:39:29AM +0200, Greg Kroah-Hartman wrote: > From: Eric Dumazet > > commit 0f6925b3e8da0dbbb52447ca8a8b42b371aac7db upstream. > > 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: Greg Kroah-Hartman 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(-) > > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -406,9 +406,13 @@ static struct sk_buff *page_to_skb(struc > 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) { > --- a/include/linux/virtio_net.h > +++ b/include/linux/virtio_net.h > @@ -65,14 +65,18 @@ static inline int virtio_net_hdr_to_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 @@ retry: > } > > 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; > } > } > _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization