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=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 6201FC4724C for ; Fri, 8 May 2020 02:06:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42D4D208D6 for ; Fri, 8 May 2020 02:06:10 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="X2lOtDhg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726904AbgEHCGJ (ORCPT ); Thu, 7 May 2020 22:06:09 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:51442 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726612AbgEHCGJ (ORCPT ); Thu, 7 May 2020 22:06:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588903568; 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=dZbF9/bTjanUhF5OVHEwVOjq8OzxNOAAj9TnQsQ5YVI=; b=X2lOtDhgTvZL+O6DMOKYALPbKIhKq78WdjLIHCDa6IVOyez4RONIAckEJfv9uV1PjdoDaN SHrMapXc1lm7YaBkF6Ta58bitKzoSFbxoN45+eqsInYEDmkr03x2iwMSR6WuVOLkRc6qrs AZ9v1BuM7GZG0LqH3TuVkG7fepZK19Y= 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-15-z4dO6uWFND20sqjohZIG_Q-1; Thu, 07 May 2020 22:06:06 -0400 X-MC-Unique: z4dO6uWFND20sqjohZIG_Q-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BFD891895957; Fri, 8 May 2020 02:06:03 +0000 (UTC) Received: from [10.72.13.98] (ovpn-13-98.pek2.redhat.com [10.72.13.98]) by smtp.corp.redhat.com (Postfix) with ESMTP id 835E269C88; Fri, 8 May 2020 02:05:47 +0000 (UTC) Subject: Re: [PATCH net-next v2 21/33] virtio_net: add XDP frame size in two code paths To: "Michael S. Tsirkin" , Jesper Dangaard Brouer Cc: sameehj@amazon.com, netdev@vger.kernel.org, bpf@vger.kernel.org, zorik@amazon.com, akiyano@amazon.com, gtzalik@amazon.com, =?UTF-8?Q?Toke_H=c3=b8iland-J=c3=b8rgensen?= , Daniel Borkmann , Alexei Starovoitov , John Fastabend , Alexander Duyck , Jeff Kirsher , David Ahern , Willem de Bruijn , Ilias Apalodimas , Lorenzo Bianconi , Saeed Mahameed , steffen.klassert@secunet.com References: <158824557985.2172139.4173570969543904434.stgit@firesoul> <158824572816.2172139.1358700000273697123.stgit@firesoul> <20200506163414-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <6e86e5de-8558-0f3b-53ce-ab0f611cc649@redhat.com> Date: Fri, 8 May 2020 10:05:46 +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: <20200506163414-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 2020/5/7 上午4:34, Michael S. Tsirkin wrote: > On Thu, Apr 30, 2020 at 01:22:08PM +0200, 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. >> >> Cc: Jason Wang >> Signed-off-by: Jesper Dangaard Brouer > Acked-by: Michael S. Tsirkin Note that we do:         xdp.data_hard_start = data - VIRTIO_XDP_HEADROOM + vi->hdr_len; So using PAGE_SIZE here is probably not correct. Thanks >