From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Samudrala, Sridhar" Subject: Re: [virtio-dev] Re: [RFC PATCH 2/3] netdev: kernel-only IFF_HIDDEN netdevice Date: Wed, 18 Apr 2018 22:00:51 -0700 Message-ID: <4e029524-d542-0f12-bfdb-7c8a2f198e28@intel.com> References: <54accf73-e6cc-e03f-6a1c-34e1bbd78047@gmail.com> <20180404.133749.1802514210170809419.davem@davemloft.net> <20180408.123207.2294740686493951200.davem@davemloft.net> <1f3af59f-fd64-cc0d-f9eb-668636c52db4@intel.com> <20180419072003-mutt-send-email-mst@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Siwei Liu , David Miller , David Ahern , Jiri Pirko , si-wei liu , Stephen Hemminger , Alexander Duyck , "Brandeburg, Jesse" , Jakub Kicinski , Jason Wang , Netdev , virtualization@lists.linux-foundation.org, virtio-dev@lists.oasis-open.org To: "Michael S. Tsirkin" Return-path: Received: from mga06.intel.com ([134.134.136.31]:3686 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752143AbeDSFAx (ORCPT ); Thu, 19 Apr 2018 01:00:53 -0400 In-Reply-To: <20180419072003-mutt-send-email-mst@kernel.org> Content-Language: en-US Sender: netdev-owner@vger.kernel.org List-ID: On 4/18/2018 9:41 PM, Michael S. Tsirkin wrote: > On Wed, Apr 18, 2018 at 04:33:34PM -0700, Samudrala, Sridhar wrote: >> On 4/17/2018 5:26 PM, Siwei Liu wrote: >>> I ran this with a few folks offline and gathered some good feedbacks >>> that I'd like to share thus revive the discussion. >>> >>> First of all, as illustrated in the reply below, cloud service >>> providers require transparent live migration. Specifically, the main >>> target of our case is to support SR-IOV live migration via kernel >>> upgrade while keeping the userspace of old distros unmodified. If it's >>> because this use case is not appealing enough for the mainline to >>> adopt, I will shut up and not continue discussing, although >>> technically it's entirely possible (and there's precedent in other >>> implementation) to do so to benefit any cloud service providers. >>> >>> If it's just the implementation of hiding netdev itself needs to be >>> improved, such as implementing it as attribute flag or adding linkdump >>> API, that's completely fine and we can look into that. However, the >>> specific issue needs to be undestood beforehand is to make transparent >>> SR-IOV to be able to take over the name (so inherit all the configs) >>> from the lower netdev, which needs some games with uevents and name >>> space reservation. So far I don't think it's been well discussed. >>> >>> One thing in particular I'd like to point out is that the 3-netdev >>> model currently missed to address the core problem of live migration: >>> migration of hardware specific feature/state, for e.g. ethtool configs >>> and hardware offloading states. Only general network state (IP >>> address, gateway, for eg.) associated with the bypass interface can be >>> migrated. As a follow-up work, bypass driver can/should be enhanced to >>> save and apply those hardware specific configs before or after >>> migration as needed. The transparent 1-netdev model being proposed as >>> part of this patch series will be able to solve that problem naturally >>> by making all hardware specific configurations go through the central >>> bypass driver, such that hardware configurations can be replayed when >>> new VF or passthrough gets plugged back in. Although that >>> corresponding function hasn't been implemented today, I'd like to >>> refresh everyone's mind that is the core problem any live migration >>> proposal should have addressed. >>> >>> If it would make things more clear to defer netdev hiding until all >>> functionalities regarding centralizing and replay are implemented, >>> we'd take advices like that and move on to implementing those features >>> as follow-up patches. Once all needed features get done, we'd resume >>> the work for hiding lower netdev at that point. Think it would be the >>> best to make everyone understand the big picture in advance before >>> going too far. >> I think we should get the 3-netdev model integrated and add any additional >> ndo_ops/ethool ops that we would like to support/migrate before looking into >> hiding the lower netdevs. > Once they are exposed, I don't think we'll be able to hide them - > they will be a kernel ABI. > > Do you think everyone needs to hide the SRIOV device? > Or that only some users need this? Hyper-V is currently supporting live migration without hiding the SR-IOV device. So i don't think it is a hard requirement. And also, as we don't yet have a consensus on how to hide the lower netdevs, we could make it as another feature bit to hide lower netdevs once we have an acceptable solution.