Re: [Xen-devel] [rfc 00/18] ioemu: use devfn instead of slots as the unit for passthrough

[Simon Horman <horms@xxxxxxxxxxxx>]

On Thu, Mar 05, 2009 at 09:22:28AM +0000, Keir Fraser wrote:
> On 05/03/2009 09:05, "Simon Horman" <horms@xxxxxxxxxxxx> wrote:
> 
> > * pass-through devices may not share a GSI with another pass-through
> >   device, and its better if they don't share a GSI with an ioemu
> >   device either
> 
> Why is such sharing disallowed? Is this a problem with mapping multiple MSI
> sources to a single level-triggered GSI? If we can reliably map one MSI to
> an emulated GSI, I would have thought that wire-ORing them would be easy,
> but perhaps the emulation is dodgy to begin with, even without sharing?

Shimada-san mentioned it in a previous post, hopefully he can explain further.

> > I can't actually get a system with this mapping to boot
> > (which prehaps means its flawed for the first few devices).
> > But a fundamental problem (e.g. for users) with using
> > such an allocation stratergy?
> 
> Yes, a sparse mapping into the devfn space is absolutely fine. Indeed you'll
> be needing to consider all that space to make efficient use of the currently
> available 32 GSIs.

Agreed

-- 
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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