From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Fri, 25 Nov 2022 07:08:14 -0500 From: "Michael S. Tsirkin" Subject: Re: [virtio-dev] Re: [PATCH v9 02/10] admin: introduce device group and related concepts Message-ID: <20221125070700-mutt-send-email-mst@kernel.org> 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> MIME-Version: 1.0 In-Reply-To: <5731c35c-f24d-3667-b3be-c2f86f849b92@redhat.com> Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit To: Jason Wang Cc: Cornelia Huck , 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 at 11:23:09AM +0800, Jason Wang wrote: > > 在 2022/11/24 20:12, Cornelia Huck 写道: > > 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 wrote: > > > > > 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 specified): > > > > > > > +\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 the > > > > > > 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 PCI > transport to describe the SR-IOV group identifier. > right so everything is in admin.tex except for the identifier which is in pci. I find this split annoying - not enough material here where splitting makes things cleaner. But we can move it down the road. > > > 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 > implemented via different transport specific registers/commands/offsets etc. > 2) I'm not quite sure there would be a transport-independent group > identifier other than the virtqueue transport, so I wonder if it makes sense > to split the id space into global ones as well as the transport specific > ones > > > > 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 > worth/correct/expensive to describe a transport specific identifier in the > basic facility part. > > Thanks > > > > > > > > --------------------------------------------------------------------- > > To unsubscribe, e-mail: virtio-dev-unsubscribe@lists.oasis-open.org > > For additional commands, e-mail: virtio-dev-help@lists.oasis-open.org > >