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

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Message-ID: <20081106180354.GA17429@kroah.com>
Date:	Thu, 6 Nov 2008 10:03:54 -0800
From:	Greg KH <greg@...ah.com>
To:	"Fischer, Anna" <anna.fischer@...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

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"?

> > 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?

> 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.

> > > I have so far only seen Yu Zhao's "7-patch" set.  I've not yet looked
> > > at his subsequently tendered "15-patch" set so I don't know what has
> > > changed.    The hardware/firmware implementation for any given SR-IOV
> > > compatible device, will determine the extent of differences required
> > > between a PF driver and a VF driver.
> >
> > Yeah, that's what I'm worried/curious about.  Without seeing the code
> > for such a driver, how can we properly evaluate if this infrastructure
> > is the correct one and the proper way to do all of this?
> 
> Yu's API allows a PF driver to register with the Linux PCI code and
> use it to activate VFs and allocate their resources. The PF driver
> needs to be modified to work with that API. While you can argue about
> how that API is supposed to look like, it is clear that such an API is
> required in some form.

I totally agree, I'm arguing about what that API looks like :)

I want to see some code...

thanks,

greg k-h
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