Re: [Qemu-devel] [PATCH 0/2] pci-assign: MSI affinity support

[Alex Williamson]

On Fri, 2013-05-10 at 14:40 +0200, Jan Kiszka wrote:
> On 2013-05-09 18:35, Alex Williamson wrote:
> > I posted these about 6 months ago and Jan felt we should implement
> > MSI notifiers like we have for MSI-X.  That still hasn't happened.
> 
> Device assignments are the only currently known users - and you provide
> this feature, so...
> 
> POWER does this nice configuration of MSI messages via a side channel.
> Not that it already fires the MSI-X notifiers properly, but a generic
> notifier based approach is the right way to abstract away the different
> modification channels (instead of encoding them at the consumer side
> like in your patches).
> 
> Moreover, having different designs for MSI and MSI-X is just ugly.

OTOH, if device assignment is the only one that needs this and it's
trivial to implement there, why would we bloat the common code with
notifiers and caching vector messages.  I'm not that thrilled with the
MSI-X notifiers to go copy them into MSI anyway, they completely miss
important things like an overall device MSI-X enable or disable.

For this much code:

 hw/i386/kvm/pci-assign.c |   78 +++++++++++++++++++++++++++++++---------------
 1 file changed, 53 insertions(+), 25 deletions(-)

we get a feature that's immediately useful to a guest.  Seems like a win
to me.  Thanks,

Alex