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 C81C0C433F5 for ; Thu, 25 Nov 2021 07:28:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233066AbhKYHbe (ORCPT ); Thu, 25 Nov 2021 02:31:34 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:24839 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230342AbhKYH3d (ORCPT ); Thu, 25 Nov 2021 02:29:33 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1637825182; 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=KCI9CPt99xPAxo4OPIihJLE+9ULo5GUcCD2zEw3zAm0=; b=MmAOUjSXwHGYgLyON40rZREWkuxvRJQzAlU4tSMhh5eNMxeNaLbCsB7MWR57ov7HNBRfbE 1LDGY+U2pRQS3FyOvwiLyVzUgcX22bQnelvoWiasyBsV5MdFor4CgibkV5nEYWRuEDjeuc NL7gKQEEY9LJ274R1S3uMdktx4YevbM= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-264-2BFixzhTMjOeNqcGTXW1Qw-1; Thu, 25 Nov 2021 02:26:21 -0500 X-MC-Unique: 2BFixzhTMjOeNqcGTXW1Qw-1 Received: by mail-wm1-f69.google.com with SMTP id z138-20020a1c7e90000000b003319c5f9164so4436377wmc.7 for ; Wed, 24 Nov 2021 23:26:21 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=KCI9CPt99xPAxo4OPIihJLE+9ULo5GUcCD2zEw3zAm0=; b=Fh44rbLuJ6GyYFQTZx/3mHYmGFSe/DUwabZpHaOG8Km0UMZuO95bvWIyLlnR8WnlVA wbFhRqhp15Ngr8Beu2TveVgN60YYBAppkc1An9fz2zt71OpMmOKOidnkgLCEDY5MSLkb 3iWh3dPs7feGesuR/JLSmd3IyX9Qz5rDnxOf0dV7t1Do4TUbCKkOPlTKfVcywJy9njK6 iHamGYolaz9QwBEbz6diNDBsgt/JUy+/vtnjJh3aad+ts0irW7IcbfKCpEU2VTXjPkTZ Tvhjca4OiyzT0BaPBoJODxHsD7LS9VSJSHikVB2WJYNf3lviaNIgbhWt8jES0EUyXDP6 Y/9g== X-Gm-Message-State: AOAM530c8LigGvPO1Y8+BQyGomPBVaaTNj2/BxswI3IuiVVrsDk/2bCX t0RaeWgVq2Akfu7CZaOY+3PWZAseZJIGt2SkOCui2H5ugtEocX7DTxfPuvyrKJH+DVojPC0nPPK Wqd5mz2cPEYdlvlJM X-Received: by 2002:adf:b18e:: with SMTP id q14mr4435686wra.477.1637825180321; Wed, 24 Nov 2021 23:26:20 -0800 (PST) X-Google-Smtp-Source: ABdhPJzM6lbQ3uDZ5zJpkNVH+bqgGz375VJK1frTc+q8xHT9a96tyQUcZyAB+1UDheXMUsphwXYylg== X-Received: by 2002:adf:b18e:: with SMTP id q14mr4435665wra.477.1637825180075; Wed, 24 Nov 2021 23:26:20 -0800 (PST) Received: from redhat.com ([45.15.18.67]) by smtp.gmail.com with ESMTPSA id f19sm9035167wmq.34.2021.11.24.23.26.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 24 Nov 2021 23:26:19 -0800 (PST) Date: Thu, 25 Nov 2021 02:26:13 -0500 From: "Michael S. Tsirkin" To: Jason Wang Cc: virtualization , netdev , linux-kernel , Eli Cohen Subject: Re: [PATCH net] virtio-net: enable big mode correctly Message-ID: <20211125022442-mutt-send-email-mst@kernel.org> References: <20211125060547.11961-1-jasowang@redhat.com> <20211125015532-mutt-send-email-mst@kernel.org> <20211125021308-mutt-send-email-mst@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, Nov 25, 2021 at 03:20:07PM +0800, Jason Wang wrote: > On Thu, Nov 25, 2021 at 3:15 PM Michael S. Tsirkin wrote: > > > > On Thu, Nov 25, 2021 at 03:11:58PM +0800, Jason Wang wrote: > > > 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. > > > > OK, even more so then. > > > > > > 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 > > > > You want to block guests from setting MTU to a value >GOOD_PACKET_LEN? > > Yes, or fix the issue to let large packets on RX work (e.g as the TODO > said, size the buffer: for <=4K mtu continue to work as > add_recvbuf_small(), for >= 4K switch to use big). Right. The difficulty is with changing modes, current code isn't designed for it. > > Maybe ... it will prevent sending large packets which did work ... > > Yes, but it's strange to allow TX but not RX > > > I'd tread carefully here, and I don't think this kind of thing is net > > material. > > I agree consider it can't be fixed easily. > > 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 > > > > > >