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[PATCH v9 00/10] Introduce device group and device management
On Fri, Nov 25, 2022 at 11:23:09AM +0800, Jason Wang wrote:
>
> ? 2022/11/24 20:12, Cornelia Huck ??:
>
> On Thu, Nov 24 2022, "Michael S. Tsirkin" <[email protected]> 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 <[email protected]> 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 <[email protected]> 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
>
>
> >
> >
> >
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