From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Sender: List-Post: List-Help: List-Unsubscribe: List-Subscribe: From: Cornelia Huck In-Reply-To: <5731c35c-f24d-3667-b3be-c2f86f849b92@redhat.com> References: <20221123210706.21476-1-mst@redhat.com> <20221123210706.21476-3-mst@redhat.com> <20221124020650-mutt-send-email-mst@kernel.org> <20221124031554-mutt-send-email-mst@kernel.org> <87h6yoh7pj.fsf@redhat.com> <5731c35c-f24d-3667-b3be-c2f86f849b92@redhat.com> Date: Fri, 25 Nov 2022 11:58:49 +0100 Message-ID: <87wn7jgv12.fsf@redhat.com> MIME-Version: 1.0 Subject: [virtio] Re: [virtio-dev] Re: [PATCH v9 02/10] admin: introduce device group and related concepts Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable To: Jason Wang , "Michael S. Tsirkin" Cc: virtio-comment@lists.oasis-open.org, virtio-dev@lists.oasis-open.org, sgarzare@redhat.com, stefanha@redhat.com, nrupal.jani@intel.com, Piotr.Uminski@intel.com, hang.yuan@intel.com, virtio@lists.oasis-open.org, Zhu Lingshan , pasic@linux.ibm.com, Shahaf Shuler , Parav Pandit , Max Gurtovoy List-ID: On Fri, Nov 25 2022, Jason Wang wrote: > =E5=9C=A8 2022/11/24 20:12, Cornelia Huck =E5=86=99=E9=81=93: >> On Thu, Nov 24 2022, "Michael S. Tsirkin" wrote: >> >>> On Thu, Nov 24, 2022 at 03:37:42PM +0800, Jason Wang wrote: >>>> On Thu, Nov 24, 2022 at 3:08 PM Michael S. Tsirkin wr= ote: >>>>> On Thu, Nov 24, 2022 at 01:41:41PM +0800, Jason Wang wrote: >>>>>> On Thu, Nov 24, 2022 at 5:08 AM Michael S. Tsirkin = wrote: >>>>>>> +The following group types, and their identifiers, are currently sp= ecified): >>>>>>> +\begin{description} >>>>>>> +\item[SR-IOV group type (0x1)] >>>>>>> +This device group has a PCI Single Root I/O Virtualization >>>>>>> +(SR-IOV) physical function (PF) device as the owner and includes >>>>>>> +all its SR-IOV virtual functions (VFs) as members (see >>>>>>> +\hyperref[intro:PCIe]{[PCIe]}). >>>>>> So I wonder what's the advantage of using a global identifier over t= he >>>>>> transport specific one. There's almost no way for CCW/MMIO to use >>>>>> SR-IOV. Limiting it to PCI seems much easier and avoids layer >>>>>> violation. >>>>>> >>>>>> Thanks >>>>> So we burn up an identifier, ccw and mmio won't be able to use it. >>>>> Big deal? Why? >>>> Because it is transport specific. The basic facility should be >>>> transport independent. >>> I tried this but the result is spread all over the spec >>> and does not result in a readable cohesive whole. > > > I may miss something, but it looks to me it's just a subsection in the=20 > PCI transport to describe the SR-IOV group identifier. > > >>> So we give up on the transport independent purity a bit and it >>> seems worth it. >>> Also explained this in the cover letter - have you seen that? > > > Sorry, I don't. > > >>> >>> >>> >>>>> And I think we might find a use for this with MMIO >>>>> down the road with some kind of passthrough. Who knows. >>>> Probably, but can it be modeled exactly as what SR-IOV looks like? Or >>>> anyhow, it's not too late to define this for MMIO at that time. For >>>> example, we know MSI-X may work for MMIO but we define it only for PCI >>>> now. >>>> >>>> Thanks >>> Right. So if we reserve the id for all transports then it will >>> be easy to do. >> Also, if we go with transport-specific ids, we might end up with >> different ids per transport when we add a future transport-independent >> feature. > > > I'm not sure this is a real problem: > > 1) all the basic facilities are now transport-independent but they are=20 > implemented via different transport specific registers/commands/offsets e= tc. Yes, but in this case we're using the same basic structure, just with a different id. I think that has a high potential for errors. > 2) I'm not quite sure there would be a transport-independent group=20 > identifier other than the virtqueue transport, so I wonder if it makes=20 > sense to split the id space into global ones as well as the transport=20 > specific ones I think global vs. transport-specific is overkill here. I don't think we expect a flood of new group types. > > >> The global id space really should be big enough to accommodate >> even single-transport groups. > > > Yes, so it's not about the space but about whether or it it's=20 > worth/correct/expensive to describe a transport specific identifier in=20 > the basic facility part. IMHO, splitting this or using transport-specific namespaces is making this complicated for not much in return. What do others think? --------------------------------------------------------------------- To unsubscribe from this mail list, you must leave the OASIS TC that=20 generates this mail. Follow this link to all your TCs in OASIS at: https://www.oasis-open.org/apps/org/workgroup/portal/my_workgroups.php=20