linux-kernel - RE: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

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Message-ID: <0199E0D51A61344794750DC57738F58E5E26F99702@GVW1118EXC.americas.hpqcorp.net>
Date:	Thu, 6 Nov 2008 20:04:27 +0000
From:	"Fischer, Anna" <anna.fischer@...com>
To:	Greg KH <greg@...ah.com>
CC:	H L <swdevyid@...oo.com>,
	"randy.dunlap@...cle.com" <randy.dunlap@...cle.com>,
	"grundler@...isc-linux.org" <grundler@...isc-linux.org>,
	"Chiang, Alexander" <achiang@...com>,
	"matthew@....cx" <matthew@....cx>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"rdreier@...co.com" <rdreier@...co.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jbarnes@...tuousgeek.org" <jbarnes@...tuousgeek.org>,
	"virtualization@...ts.linux-foundation.org" 
	<virtualization@...ts.linux-foundation.org>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"mingo@...e.hu" <mingo@...e.hu>
Subject: RE: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

> Subject: Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support
>
> On Thu, Nov 06, 2008 at 05:38:16PM +0000, Fischer, Anna wrote:
> > > On Thu, Nov 06, 2008 at 08:41:53AM -0800, H L wrote:
> > > > I have not modified any existing drivers, but instead I threw
> > > together
> > > > a bare-bones module enabling me to make a call to
> pci_iov_register()
> > > > and then poke at an SR-IOV adapter's /sys entries for which no
> driver
> > > > was loaded.
> > > >
> > > > It appears from my perusal thus far that drivers using these new
> > > > SR-IOV patches will require modification; i.e. the driver
> associated
> > > > with the Physical Function (PF) will be required to make the
> > > > pci_iov_register() call along with the requisite notify()
> function.
> > > > Essentially this suggests to me a model for the PF driver to
> perform
> > > > any "global actions" or setup on behalf of VFs before enabling
> them
> > > > after which VF drivers could be associated.
> > >
> > > Where would the VF drivers have to be associated?  On the "pci_dev"
> > > level or on a higher one?
> >
> > A VF appears to the Linux OS as a standard (full, additional) PCI
> > device. The driver is associated in the same way as for a normal PCI
> > device. Ideally, you would use SR-IOV devices on a virtualized
> system,
> > for example, using Xen. A VF can then be assigned to a guest domain
> as
> > a full PCI device.
>
> It's that "second" part that I'm worried about.  How is that going to
> happen?  Do you have any patches that show this kind of "assignment"?

That depends on your setup. Using Xen, you could assign the VF to a guest domain like any other PCI device, e.g. using PCI pass-through. For VMware, KVM, there are standard ways to do that, too. I currently don't see why SR-IOV devices would need any specific, non-standard mechanism for device assignment.


> > > Will all drivers that want to bind to a "VF" device need to be
> > > rewritten?
> >
> > Currently, any vendor providing a SR-IOV device needs to provide a PF
> > driver and a VF driver that runs on their hardware.
>
> Are there any such drivers available yet?

I don't know.


> > A VF driver does not necessarily need to know much about SR-IOV but
> > just run on the presented PCI device. You might want to have a
> > communication channel between PF and VF driver though, for various
> > reasons, if such a channel is not provided in hardware.
>
> Agreed, but what does that channel look like in Linux?
>
> I have some ideas of what I think it should look like, but if people
> already have code, I'd love to see that as well.

At this point I would guess that this code is vendor specific, as are the drivers. The issue I see is that most likely drivers will run in different environments, for example, in Xen the PF driver runs in a driver domain while a VF driver runs in a guest VM. So a communication channel would need to be either Xen specific, or vendor specific. Also, a guest using the VF might run Windows while the PF might be controlled under Linux.

Anna
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