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

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Date:	Fri, 7 Nov 2008 09:24:08 +1100
From:	Simon Horman <horms@...ge.net.au>
To:	Greg KH <greg@...ah.com>
Cc:	Matthew Wilcox <matthew@....cx>, H L <swdevyid@...oo.com>,
	Yu Zhao <yu.zhao@...el.com>, randy.dunlap@...cle.com,
	grundler@...isc-linux.org, achiang@...com,
	linux-pci@...r.kernel.org, rdreier@...co.com,
	linux-kernel@...r.kernel.org, jbarnes@...tuousgeek.org,
	virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
	mingo@...e.hu, Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

On Thu, Nov 06, 2008 at 09:53:08AM -0800, Greg KH wrote:
> On Thu, Nov 06, 2008 at 10:47:41AM -0700, Matthew Wilcox wrote:
> > On Thu, Nov 06, 2008 at 08:49:19AM -0800, Greg KH 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?
> > > 
> > > Will all drivers that want to bind to a "VF" device need to be
> > > rewritten?
> > 
> > The current model being implemented by my colleagues has separate
> > drivers for the PF (aka native) and VF devices.  I don't personally
> > believe this is the correct path, but I'm reserving judgement until I
> > see some code.
> 
> Hm, I would like to see that code before we can properly evaluate this
> interface.  Especially as they are all tightly tied together.
> 
> > I don't think we really know what the One True Usage model is for VF
> > devices.  Chris Wright has some ideas, I have some ideas and Yu Zhao has
> > some ideas.  I bet there's other people who have other ideas too.
> 
> I'd love to hear those ideas.
> 
> Rumor has it, there is some Xen code floating around to support this
> already, is that true?

Xen patches were posted to xen-devel by Yu Zhao on the 29th of September [1].
Unfortunately the only responses that I can find are a) that the patches
were mangled and b) they seem to include changes (by others) that have
been merged into Linux. I have confirmed that both of these concerns
are valid.

I have not yet examined the difference, if any, in the approach taken by Yu
to SR-IOV in Linux and Xen. Unfortunately comparison is less than trivial
due to the gaping gap in kernel versions between Linux-Xen (2.6.18.8) and
Linux itself.

One approach that I was considering in order to familiarise myself with the
code was to backport the v6 Linux patches (this thread) to Linux-Xen. I made a
start on that, but again due to kernel version differences it is non-trivial.

[1] http://lists.xensource.com/archives/html/xen-devel/2008-09/msg00923.html

-- 
Simon Horman
  VA Linux Systems Japan K.K., Sydney, Australia Satellite Office
  H: www.vergenet.net/~horms/             W: www.valinux.co.jp/en

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