From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by dpdk.org (Postfix) with ESMTP id C2FA7B6D for ; Mon, 28 Nov 2016 16:29:04 +0100 (CET) Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 00FA781239; Mon, 28 Nov 2016 15:29:04 +0000 (UTC) Received: from [10.36.7.160] (vpn1-7-160.ams2.redhat.com [10.36.7.160]) by int-mx09.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id uASFSwQX009844 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO); Mon, 28 Nov 2016 10:29:00 -0500 To: "Kavanagh, Mark B" , Kevin Traynor , Yuanhan Liu , "Weglicki, MichalX" References: <20161011173526-mutt-send-email-mst@kernel.org> <20161117082902.GM5048@yliu-dev.sh.intel.com> <20161117094936.GN5048@yliu-dev.sh.intel.com> <20161117192445-mutt-send-email-mst@kernel.org> <20161122130223.GW5048@yliu-dev.sh.intel.com> <20161122164143-mutt-send-email-mst@kernel.org> <20161124063129.GE5048@yliu-dev.sh.intel.com> <4d6e8cf0-fe19-43a9-ff73-c2a9cdeb681e@redhat.com> <20161124123304.GG5048@yliu-dev.sh.intel.com> <0f83baa0-206e-4af2-1a97-d59c8e0582b8@redhat.com> Cc: "Michael S. Tsirkin" , "dev@dpdk.org" , Stephen Hemminger , "qemu-devel@nongnu.org" , "libvir-list@redhat.com" , "vpp-dev@lists.fd.io" , =?UTF-8?Q?Marc-Andr=c3=a9_Lureau?= From: Maxime Coquelin Message-ID: <67cfb109-8729-916e-5535-80af620bafe5@redhat.com> Date: Mon, 28 Nov 2016 16:28:58 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.68 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Mon, 28 Nov 2016 15:29:04 +0000 (UTC) Subject: Re: [dpdk-dev] dpdk/vpp and cross-version migration for vhost X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: patches and discussions about DPDK List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 28 Nov 2016 15:29:05 -0000 On 11/24/2016 04:24 PM, Kavanagh, Mark B wrote: >> >> On 11/24/2016 12:47 PM, Maxime Coquelin wrote: >>> >>> >>> On 11/24/2016 01:33 PM, Yuanhan Liu wrote: >>>> On Thu, Nov 24, 2016 at 09:30:49AM +0000, Kevin Traynor wrote: >>>>>> On 11/24/2016 06:31 AM, Yuanhan Liu wrote: >>>>>>>> On Tue, Nov 22, 2016 at 04:53:05PM +0200, Michael S. Tsirkin wrote: >>>>>>>>>>>>>> You keep assuming that you have the VM started first and >>>>>>>>>>>>>> figure out things afterwards, but this does not work. >>>>>>>>>>>>>> >>>>>>>>>>>>>> Think about a cluster of machines. You want to start a VM in >>>>>>>>>>>>>> a way that will ensure compatibility with all hosts >>>>>>>>>>>>>> in a cluster. >>>>>>>>>>>> >>>>>>>>>>>> I see. I was more considering about the case when the dst >>>>>>>>>>>> host (including the qemu and dpdk combo) is given, and >>>>>>>>>>>> then determine whether it will be a successfull migration >>>>>>>>>>>> or not. >>>>>>>>>>>> >>>>>>>>>>>> And you are asking that we need to know which host could >>>>>>>>>>>> be a good candidate before starting the migration. In such >>>>>>>>>>>> case, we indeed need some inputs from both the qemu and >>>>>>>>>>>> vhost-user backend. >>>>>>>>>>>> >>>>>>>>>>>> For DPDK, I think it could be simple, just as you said, it >>>>>>>>>>>> could be either a tiny script, or even a macro defined in >>>>>>>>>>>> the source code file (we extend it every time we add a >>>>>>>>>>>> new feature) to let the libvirt to read it. Or something >>>>>>>>>>>> else. >>>>>>>>>> >>>>>>>>>> There's the issue of APIs that tweak features as Maxime >>>>>>>>>> suggested. >>>>>>>> >>>>>>>> Yes, it's a good point. >>>>>>>> >>>>>>>>>> Maybe the only thing to do is to deprecate it, >>>>>>>> >>>>>>>> Looks like so. >>>>>>>> >>>>>>>>>> but I feel some way for application to pass info into >>>>>>>>>> guest might be benefitial. >>>>>>>> >>>>>>>> The two APIs are just for tweaking feature bits DPDK supports >>>>>> before >>>>>>>> any device got connected. It's another way to disable some features >>>>>>>> (the another obvious way is to through QEMU command lines). >>>>>>>> >>>>>>>> IMO, it's bit handy only in a case like: we have bunch of VMs. >>>>>> Instead >>>>>>>> of disabling something though qemu one by one, we could disable it >>>>>>>> once in DPDK. >>>>>>>> >>>>>>>> But I doubt the useful of it. It's only used in DPDK's vhost >>>>>> example >>>>>>>> after all. Nor is it used in vhost pmd, neither is it used in OVS. >>>>>> >>>>>> rte_vhost_feature_disable() is currently used in OVS, >>>>> lib/netdev-dpdk.c >>>> Hmmm. I must have checked very old code ... >>>>>> >>>>>> netdev_dpdk_vhost_class_init(void) >>>>>> { >>>>>> static struct ovsthread_once once = OVSTHREAD_ONCE_INITIALIZER; >>>>>> >>>>>> /* This function can be called for different classes. The >>>>>> initialization >>>>>> * needs to be done only once */ >>>>>> if (ovsthread_once_start(&once)) { >>>>>> rte_vhost_driver_callback_register(&virtio_net_device_ops); >>>>>> rte_vhost_feature_disable(1ULL << VIRTIO_NET_F_HOST_TSO4 >>>>>> | 1ULL << VIRTIO_NET_F_HOST_TSO6 >>>>>> | 1ULL << VIRTIO_NET_F_CSUM); >>>> I saw the commit introduced such change, but it tells no reason why >>>> it was added. >>> >>> I'm also interested to know the reason. >> >> I can't remember off hand, added Mark K or Michal W who should be able >> to shed some light on it. > > DPDK v16.04 added support for vHost User TSO; as such, by default, TSO is advertised to guest devices as an available feature during feature negotiation with QEMU. > However, while the vHost user backend sets up the majority of the mbuf fields that are required for TSO, there is still a reliance on the associated DPDK application (i.e. in this case OvS-DPDK) to set the remaining flags and/or offsets. Since OvS-DPDK doesn't currently provide that functionality, it is necessary to explicitly disable TSO; otherwise, undefined behaviour will ensue. Thanks Mark for the clarification. In this case, maybe we could add a DPDK build option to disable Vhost's TSO support, that would be selected for OVS packages? Does that sound reasonable? Cheers, Maxime >> >>> In any case, I think this is something that can/should be managed by >>> the management tool, which should disable it in cmd parameters. >>> >>> Kevin, do you agree? >> >> I think best to find out the reason first. Because if no reason to >> disable in the code, then no need to debate! >> >>> >>> Cheers, >>> Maxime >