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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 D20B4C38A2A for ; Sat, 9 May 2020 02:15:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AA6E421655 for ; Sat, 9 May 2020 02:15:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="WcuuAKjq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728385AbgEICPt (ORCPT ); Fri, 8 May 2020 22:15:49 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:31697 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727878AbgEICPs (ORCPT ); Fri, 8 May 2020 22:15:48 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588990546; 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=35W7f4O3N2+IVnSePhHRorinIZLPPaeJSjwnMIh6Cys=; b=WcuuAKjqZza8H8MbNTJtMzLHHrKoDGI4i4/66/Z7mc4Z+oI10KH5e/Pmqbt25hS4EgSpcs 3lJhxg/JYUs8dNJs/3JXwnQ04F94CoA/Mk1aIqhnVO1VJvdfyFcQNGpm7CRusKLcrRMFj5 dL0Ta0O3VqV0JWblma3Ys4l+kQPjhLU= 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-155-e6haWJxkOoGTXPXc61Zyiw-1; Fri, 08 May 2020 22:15:42 -0400 X-MC-Unique: e6haWJxkOoGTXPXc61Zyiw-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 6C7A180058A; Sat, 9 May 2020 02:15:40 +0000 (UTC) Received: from [10.72.13.128] (ovpn-13-128.pek2.redhat.com [10.72.13.128]) by smtp.corp.redhat.com (Postfix) with ESMTP id 50B415C3FA; Sat, 9 May 2020 02:15:29 +0000 (UTC) Subject: Re: [PATCH net-next v3 21/33] virtio_net: add XDP frame size in two code paths To: Jesper Dangaard Brouer , sameehj@amazon.com Cc: netdev@vger.kernel.org, bpf@vger.kernel.org, =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= , Daniel Borkmann , Alexei Starovoitov , "David S. Miller" , John Fastabend , Alexander Duyck , Jeff Kirsher , David Ahern , Ilias Apalodimas , Lorenzo Bianconi , Saeed Mahameed , Tariq Toukan References: <158893607924.2321140.16117992313983615627.stgit@firesoul> <158893623266.2321140.16885343338278337243.stgit@firesoul> From: Jason Wang Message-ID: Date: Sat, 9 May 2020 10:15:27 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <158893623266.2321140.16885343338278337243.stgit@firesoul> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: bpf-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 2020/5/8 下午7:10, Jesper Dangaard Brouer wrote: > The virtio_net driver is running inside the guest-OS. There are two > XDP receive code-paths in virtio_net, namely receive_small() and > receive_mergeable(). The receive_big() function does not support XDP. > > In receive_small() the frame size is available in buflen. The buffer > backing these frames are allocated in add_recvbuf_small() with same > size, except for the headroom, but tailroom have reserved room for > skb_shared_info. The headroom is encoded in ctx pointer as a value. > > In receive_mergeable() the frame size is more dynamic. There are two > basic cases: (1) buffer size is based on a exponentially weighted > moving average (see DECLARE_EWMA) of packet length. Or (2) in case > virtnet_get_headroom() have any headroom then buffer size is > PAGE_SIZE. The ctx pointer is this time used for encoding two values; > the buffer len "truesize" and headroom. In case (1) if the rx buffer > size is underestimated, the packet will have been split over more > buffers (num_buf info in virtio_net_hdr_mrg_rxbuf placed in top of > buffer area). If that happens the XDP path does a xdp_linearize_page > operation. > > V3: Adjust frame_sz in receive_mergeable() case, spotted by Jason Wang. > > The code is really hard to follow, Yes, I plan to rework to make it more easier for reviewers. > so some hints to reviewers. > The receive_mergeable() case gets frames that were allocated in > add_recvbuf_mergeable() which uses headroom=virtnet_get_headroom(), > and 'buf' ptr is advanced this headroom. The headroom can only > be 0 or VIRTIO_XDP_HEADROOM, as virtnet_get_headroom is really > simple: > > static unsigned int virtnet_get_headroom(struct virtnet_info *vi) > { > return vi->xdp_queue_pairs ? VIRTIO_XDP_HEADROOM : 0; > } > > As frame_sz is an offset size from xdp.data_hard_start, reviewers > should notice how this is calculated in receive_mergeable(): > > int offset = buf - page_address(page); > [...] > data = page_address(xdp_page) + offset; > xdp.data_hard_start = data - VIRTIO_XDP_HEADROOM + vi->hdr_len; > > The calculated offset will always be VIRTIO_XDP_HEADROOM when > reaching this code. Thus, xdp.data_hard_start will be page-start > address plus vi->hdr_len. Given this xdp.frame_sz need to be > reduced with vi->hdr_len size. > > IMHO a followup patch should cleanup this code to make it easier > to maintain and understand, but it is outside the scope of this > patchset. > > Cc: Jason Wang > Signed-off-by: Jesper Dangaard Brouer > Acked-by: Michael S. Tsirkin Acked-by: Jason Wang Thanks > --- > drivers/net/virtio_net.c | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 11f722460513..9e1b5d748586 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -689,6 +689,7 @@ static struct sk_buff *receive_small(struct net_device *dev, > xdp.data_end = xdp.data + len; > xdp.data_meta = xdp.data; > xdp.rxq = &rq->xdp_rxq; > + xdp.frame_sz = buflen; > orig_data = xdp.data; > act = bpf_prog_run_xdp(xdp_prog, &xdp); > stats->xdp_packets++; > @@ -797,10 +798,11 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, > int offset = buf - page_address(page); > struct sk_buff *head_skb, *curr_skb; > struct bpf_prog *xdp_prog; > - unsigned int truesize; > + unsigned int truesize = mergeable_ctx_to_truesize(ctx); > unsigned int headroom = mergeable_ctx_to_headroom(ctx); > - int err; > unsigned int metasize = 0; > + unsigned int frame_sz; > + int err; > > head_skb = NULL; > stats->bytes += len - vi->hdr_len; > @@ -821,6 +823,11 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, > if (unlikely(hdr->hdr.gso_type)) > goto err_xdp; > > + /* Buffers with headroom use PAGE_SIZE as alloc size, > + * see add_recvbuf_mergeable() + get_mergeable_buf_len() > + */ > + frame_sz = headroom ? PAGE_SIZE : truesize; > + > /* This happens when rx buffer size is underestimated > * or headroom is not enough because of the buffer > * was refilled before XDP is set. This should only > @@ -834,6 +841,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, > page, offset, > VIRTIO_XDP_HEADROOM, > &len); > + frame_sz = PAGE_SIZE; > + > if (!xdp_page) > goto err_xdp; > offset = VIRTIO_XDP_HEADROOM; > @@ -850,6 +859,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, > xdp.data_end = xdp.data + (len - vi->hdr_len); > xdp.data_meta = xdp.data; > xdp.rxq = &rq->xdp_rxq; > + xdp.frame_sz = frame_sz - vi->hdr_len; > > act = bpf_prog_run_xdp(xdp_prog, &xdp); > stats->xdp_packets++; > @@ -924,7 +934,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev, > } > rcu_read_unlock(); > > - truesize = mergeable_ctx_to_truesize(ctx); > if (unlikely(len > truesize)) { > pr_debug("%s: rx error: len %u exceeds truesize %lu\n", > dev->name, len, (unsigned long)ctx); > >