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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E0AD1C433FE for ; Thu, 25 Nov 2021 07:14:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351325AbhKYHRZ (ORCPT ); Thu, 25 Nov 2021 02:17:25 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:29945 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1353354AbhKYHPY (ORCPT ); Thu, 25 Nov 2021 02:15:24 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1637824332; 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=nC8TAYilw4eO6qk6TmC4Zgxkm1cFgxZk3ttBumo2rHs=; b=S3MGCFb6U4mxvisdvaGyiI9kFg2FK9OSMERFeCbmEwAxR3HdsQ3XLjoeCI8nkwsjyQCWFD ZeQIovvyYygUlI0y32fnQLgJTlVYuwXF4HPVz2bsq1F5JCf1o3vmvacpASqfFrkbMl4ids yfsKnUhbS0GZyKhQH+uOEFw6qo11r8g= Received: from mail-lj1-f198.google.com (mail-lj1-f198.google.com [209.85.208.198]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-97-JYa33bVhOBiSYLOxBt0d1A-1; Thu, 25 Nov 2021 02:12:10 -0500 X-MC-Unique: JYa33bVhOBiSYLOxBt0d1A-1 Received: by mail-lj1-f198.google.com with SMTP id u28-20020a2ea17c000000b0021126b5cca2so1557961ljl.19 for ; Wed, 24 Nov 2021 23:12:10 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=nC8TAYilw4eO6qk6TmC4Zgxkm1cFgxZk3ttBumo2rHs=; b=AN0/p5AYedskPpWvNtJCqdS0xFZ3sS8JDh8BNjkUk+athtUc4y7hK4H/CSwNw1T25z sKHDfvbEh9ZVRQFKwnltpU2+KMfeBOjz7qZRRqE3qQ/mpefumF7Mg01e+n29ghO2xHFY 1C98OH5Wei4MHNBF4sErKvhA+6DNcaz5EXfIw0OKjUDHMNrQPvViYvBDqvqwx+sz7ybf Nb5P6chU6ff5JutYhi4IeG7IThaWtjsueCpiDQ4f0sq7YFycF8/f2c+QaUZM1jfHJFar pWKMwMqf0FW/eKLS753v8RQEYKWsfrUoomwVAp2t7fWymCvWPi2Ctt5gnMxDgzPN7dW7 H/Pw== X-Gm-Message-State: AOAM531QrkIaRUUAoGSIEzmcsA+3zJafzi5UmyaaA8wmj6m14kx5FZPq ke1it+y1LxGYc5kGTDiW/1GgeESOhq6XjH/meFZt1nAlYcSoq6Hpq7CtFUKnK9KJloR8r3bsRZJ RylHCH0NF37gbyQhS9V5P71WEot1s5+6nhD5fx92p X-Received: by 2002:a2e:915a:: with SMTP id q26mr22426552ljg.277.1637824329433; Wed, 24 Nov 2021 23:12:09 -0800 (PST) X-Google-Smtp-Source: ABdhPJxeFz9HHABX6i5h6gRcn7nboD1zkLDLVn4pgHX8pSwTiW54CFKdWcSQ/ukSK+/hSpgPW0KT1r7HGC5agHABEKc= X-Received: by 2002:a2e:915a:: with SMTP id q26mr22426527ljg.277.1637824329157; Wed, 24 Nov 2021 23:12:09 -0800 (PST) MIME-Version: 1.0 References: <20211125060547.11961-1-jasowang@redhat.com> <20211125015532-mutt-send-email-mst@kernel.org> In-Reply-To: <20211125015532-mutt-send-email-mst@kernel.org> From: Jason Wang Date: Thu, 25 Nov 2021 15:11:58 +0800 Message-ID: Subject: Re: [PATCH net] virtio-net: enable big mode correctly To: "Michael S. Tsirkin" Cc: virtualization , netdev , linux-kernel , Eli Cohen Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 25, 2021 at 3:00 PM Michael S. Tsirkin wrote: > > On Thu, Nov 25, 2021 at 02:05:47PM +0800, Jason Wang wrote: > > When VIRTIO_NET_F_MTU feature is not negotiated, we assume a very > > large max_mtu. In this case, using small packet mode is not correct > > since it may breaks the networking when MTU is grater than > > ETH_DATA_LEN. > > > > To have a quick fix, simply enable the big packet mode when > > VIRTIO_NET_F_MTU is not negotiated. > > This will slow down dpdk hosts which disable mergeable buffers > and send standard MTU sized packets. > > > We can do optimization on top. > > I don't think it works like this, increasing mtu > from guest >4k never worked, Looking at add_recvbuf_small() it's actually GOOD_PACKET_LEN if I was not wrong. > we can't regress everyone's > performance with a promise to maybe sometime bring it back. So consider it never work before I wonder if we can assume a 1500 as max_mtu value instead of simply using MAX_MTU? Thanks > > > Reported-by: Eli Cohen > > Cc: Eli Cohen > > Signed-off-by: Jason Wang > > > > --- > > drivers/net/virtio_net.c | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > > index 7c43bfc1ce44..83ae3ef5eb11 100644 > > --- a/drivers/net/virtio_net.c > > +++ b/drivers/net/virtio_net.c > > @@ -3200,11 +3200,12 @@ static int virtnet_probe(struct virtio_device *vdev) > > dev->mtu = mtu; > > dev->max_mtu = mtu; > > > > - /* TODO: size buffers correctly in this case. */ > > - if (dev->mtu > ETH_DATA_LEN) > > - vi->big_packets = true; > > } > > > > + /* TODO: size buffers correctly in this case. */ > > + if (dev->max_mtu > ETH_DATA_LEN) > > + vi->big_packets = true; > > + > > if (vi->any_header_sg) > > dev->needed_headroom = vi->hdr_len; > > > > -- > > 2.25.1 >