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

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Message-ID: <20081107061007.GB3860@kroah.com>
Date:	Thu, 6 Nov 2008 22:10:07 -0800
From:	Greg KH <greg@...ah.com>
To:	Chris Wright <chrisw@...s-sol.org>
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
Subject: Re: [PATCH 0/16 v6] PCI: Linux kernel SR-IOV support

On Thu, Nov 06, 2008 at 03:54:06PM -0800, Chris Wright wrote:
> * Greg KH (greg@...ah.com) 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.
> 
> First there's the question of how to represent the VF on the host.
> Ideally (IMO) this would show up as a normal interface so that normal tools
> can configure the interface.  This is not exactly how the first round of
> patches were designed.
> 
> Second there's the question of reserving the BDF on the host such that
> we don't have two drivers (one in the host and one in a guest) trying to
> drive the same device (an issue that shows up for device assignment as
> well as VF assignment).
> 
> Third there's the question of whether the VF can be used in the host at
> all.
> 
> Fourth there's the question of whether the VF and PF drivers are the
> same or separate.
> 
> The typical usecase is assigning the VF to the guest directly, so
> there's only enough functionality in the host side to allocate a VF,
> configure it, and assign it (and propagate AER).  This is with separate
> PF and VF driver.
> 
> As Anthony mentioned, we are interested in allowing the host to use the
> VF.  This could be useful for containers as well as dedicating a VF (a
> set of device resources) to a guest w/out passing it through.

All of this looks great.  So, with all of these questions, how does the
current code pertain to these issues?  It seems like we have a long way
to go...

thanks,

greg k-h
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