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Fri, 11 Sep 2020 10:08:23 +0000 (UTC) Received: from gondolin (ovpn-112-170.ams2.redhat.com [10.36.112.170]) by smtp.corp.redhat.com (Postfix) with ESMTP id CDDA57E8F2; Fri, 11 Sep 2020 10:08:09 +0000 (UTC) Date: Fri, 11 Sep 2020 12:08:06 +0200 From: Cornelia Huck To: Yan Zhao Cc: Alex Williamson , Sean Mooney , "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: <20200911120806.5cfe203c.cohuck@redhat.com> In-Reply-To: <20200911005559.GA3932@joy-OptiPlex-7040> References: <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> <20200910120244.71e7b630@w520.home> <20200911005559.GA3932@joy-OptiPlex-7040> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Fri, 11 Sep 2020 08:56:00 +0800 Yan Zhao wrote: > On Thu, Sep 10, 2020 at 12:02:44PM -0600, Alex Williamson wrote: > > On Thu, 10 Sep 2020 13:50:11 +0100 > > Sean Mooney wrote: > > =20 > > > On Thu, 2020-09-10 at 14:38 +0200, Cornelia Huck wrote: =20 > > > > On Wed, 9 Sep 2020 10:13:09 +0800 > > > > Yan Zhao wrote: > > > > =20 > > > > > > > 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 compatib= ility. > > > > > > > e.g. > > > > > > > an old generation device may have a mdev type xxx-v4-yyy, whi= le 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. =20 > > > > > >=20 > > > > > > If you want to support migration from v4 to v5, can't the (pres= umably > > > > > > newer) driver that supports v5 simply register the v4 type as w= ell, so > > > > > > that the mdev can be created as v4? (Just like QEMU versioned m= achine > > > > > > types work.) =20 > > > > >=20 > > > > > yes, it should work in some conditions. > > > > > but it may not be that good in some cases when v5 and v4 in the n= ame string > > > > > of mdev type identify hardware generation (e.g. v4 for gen8, and = v5 for > > > > > gen9) > > > > >=20 > > > > > 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 ha= rdware > > > > > differences. =20 > > > >=20 > > > > 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. > > > > =20 > > > > > then after software upgrade, v5 is now compatible to v4, should t= he > > > > > software now downgrade mdev type from v5 to v4? > > > > > not sure if moving hardware generation info into a separate attri= bute > > > > > from mdev type name is better. e.g. remove v4, v5 in mdev type, w= hile use > > > > > compatible_pci_ids to identify compatibility. =20 > > > >=20 > > > > If the generations are compatible, don't mention it in the mdev typ= e. > > > > If they aren't, use distinct types, so that management software doe= sn't > > > > have to guess. At least that would be my naive approach here. =20 [*] =20 > > > yep that is what i would prefer to see too. =20 > > > > =20 > > > > >=20 > > > > > (2) name string of mdev type is composed by "driver_name + type_n= ame". > > > > > in some devices, e.g. qat, different generations of devices are b= inding 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". =20 > > > >=20 > > > > I guess that shows a shortcoming of that "driver_name + type_name" > > > > approach? Or maybe I'm just confused. =20 > > > yes i really dont like haveing the version in the mdev-type name=20 > > > 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 q= at-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 imp= ortant however to make sure that your mdev-types > > > dont colide with other vendeors mdev types. so i woudl encurage all v= endors to prefix there mdev types with etiher the > > > device name or the vendor. =20 > >=20 > > +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, =20 >=20 > hi Alex, > got it. so do you suggest that vendors use consistent driver name over > generations of devices? > for qat, they create different modules for each generation. This > practice is not good if they want to support migration between devices > of different generations, right? Even if they create different modules, I'd assume that they have some kind of core with common functionality. I'd assume that as long they do any type registrations satisfying [*] in the core, they should be good. > and can I understand that we don't want support of migration between > different mdev types even in future ? =46rom my point of view, I don't see anything that migration between different mdev types would buy that is worth the complexity in finding out which mdev types are actually compatible.