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Thu, 10 Sep 2020 18:02:52 +0000 (UTC) Received: from w520.home (ovpn-112-71.phx2.redhat.com [10.3.112.71]) by smtp.corp.redhat.com (Postfix) with ESMTP id 097C981C40; Thu, 10 Sep 2020 18:02:44 +0000 (UTC) Date: Thu, 10 Sep 2020 12:02:44 -0600 From: Alex Williamson To: Sean Mooney Cc: Cornelia Huck , Yan Zhao , "Daniel =?UTF-8?B?UC5CZXJyYW5nw6k=?=" , kvm@vger.kernel.org, libvir-list@redhat.com, Jason Wang , qemu-devel@nongnu.org, kwankhede@nvidia.com, eauger@redhat.com, xin-ran.wang@intel.com, corbet@lwn.net, openstack-discuss@lists.openstack.org, shaohe.feng@intel.com, kevin.tian@intel.com, Parav Pandit , jian-feng.ding@intel.com, dgilbert@redhat.com, zhenyuw@linux.intel.com, hejie.xu@intel.com, bao.yumeng@zte.com.cn, intel-gvt-dev@lists.freedesktop.org, eskultet@redhat.com, Jiri Pirko , dinechin@redhat.com, devel@ovirt.org Subject: Re: device compatibility interface for live migration with assigned devices Message-ID: <20200910120244.71e7b630@w520.home> In-Reply-To: <7cebcb6c8d1a1452b43e8358ee6ee18a150a0238.camel@redhat.com> References: <20200818113652.5d81a392.cohuck@redhat.com> <20200820003922.GE21172@joy-OptiPlex-7040> <20200819212234.223667b3@x1.home> <20200820031621.GA24997@joy-OptiPlex-7040> <20200825163925.1c19b0f0.cohuck@redhat.com> <20200826064117.GA22243@joy-OptiPlex-7040> <20200828154741.30cfc1a3.cohuck@redhat.com> <8f5345be73ebf4f8f7f51d6cdc9c2a0d8e0aa45e.camel@redhat.com> <20200831044344.GB13784@joy-OptiPlex-7040> <20200908164130.2fe0d106.cohuck@redhat.com> <20200909021308.GA1277@joy-OptiPlex-7040> <20200910143822.2071eca4.cohuck@redhat.com> <7cebcb6c8d1a1452b43e8358ee6ee18a150a0238.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Thu, 10 Sep 2020 13:50:11 +0100 Sean Mooney wrote: > On Thu, 2020-09-10 at 14:38 +0200, Cornelia Huck wrote: > > On Wed, 9 Sep 2020 10:13:09 +0800 > > Yan Zhao wrote: > > > > > > > still, I'd like to put it more explicitly to make ensure it's not missed: > > > > > the reason we want to specify compatible_type as a trait and check > > > > > whether target compatible_type is the superset of source > > > > > compatible_type is for the consideration of backward compatibility. > > > > > e.g. > > > > > an old generation device may have a mdev type xxx-v4-yyy, while a newer > > > > > generation device may be of mdev type xxx-v5-yyy. > > > > > with the compatible_type traits, the old generation device is still > > > > > able to be regarded as compatible to newer generation device even their > > > > > mdev types are not equal. > > > > > > > > If you want to support migration from v4 to v5, can't the (presumably > > > > newer) driver that supports v5 simply register the v4 type as well, so > > > > that the mdev can be created as v4? (Just like QEMU versioned machine > > > > types work.) > > > > > > yes, it should work in some conditions. > > > but it may not be that good in some cases when v5 and v4 in the name string > > > of mdev type identify hardware generation (e.g. v4 for gen8, and v5 for > > > gen9) > > > > > > e.g. > > > (1). when src mdev type is v4 and target mdev type is v5 as > > > software does not support it initially, and v4 and v5 identify hardware > > > differences. > > > > My first hunch here is: Don't introduce types that may be compatible > > later. Either make them compatible, or make them distinct by design, > > and possibly add a different, compatible type later. > > > > > then after software upgrade, v5 is now compatible to v4, should the > > > software now downgrade mdev type from v5 to v4? > > > not sure if moving hardware generation info into a separate attribute > > > from mdev type name is better. e.g. remove v4, v5 in mdev type, while use > > > compatible_pci_ids to identify compatibility. > > > > If the generations are compatible, don't mention it in the mdev type. > > If they aren't, use distinct types, so that management software doesn't > > have to guess. At least that would be my naive approach here. > yep that is what i would prefer to see too. > > > > > > > > (2) name string of mdev type is composed by "driver_name + type_name". > > > in some devices, e.g. qat, different generations of devices are binding to > > > drivers of different names, e.g. "qat-v4", "qat-v5". > > > then though type_name is equal, mdev type is not equal. e.g. > > > "qat-v4-type1", "qat-v5-type1". > > > > I guess that shows a shortcoming of that "driver_name + type_name" > > approach? Or maybe I'm just confused. > yes i really dont like haveing the version in the mdev-type name > i would stongly perfger just qat-type-1 wehere qat is just there as a way of namespacing. > although symmetric-cryto, asymmetric-cryto and compression woudl be a better name then type-1, type-2, type-3 if > that is what they would end up mapping too. e.g. qat-compression or qat-aes is a much better name then type-1 > higher layers of software are unlikely to parse the mdev names but as a human looking at them its much eaiser to > understand if the names are meaningful. the qat prefix i think is important however to make sure that your mdev-types > dont colide with other vendeors mdev types. so i woudl encurage all vendors to prefix there mdev types with etiher the > device name or the vendor. +1 to all this, the mdev type is meant to indicate a software compatible interface, if different hardware versions can be software compatible, then don't make the job of finding a compatible device harder. The full type is a combination of the vendor driver name plus the vendor provided type name specifically in order to provide a type namespace per vendor driver. That's done at the mdev core level. Thanks, Alex