[vfio-users] vfio, xeon e3s, acs, & gpus -- oh my!

[Alex Williamson]

On Fri, 31 Mar 2017 13:36:36 -0700
Joshua Hoblitt <josh at hoblitt.com> wrote:

> On 03/31/2017 01:22 PM, Alex Williamson wrote:
> >> which does claim ACS support in the overview sheet. Does anyone know if
> >> ACS is indeed working with the "pex 8747" and/or the sm x1?sat series of
> >> motherboards?  Alternatively, does anyone know of an E3-1200 motherboard
> >> that does have working ACS with 2x [8x/16x] PCIe slots?  
> > The end-to-end topology needs to support ACS, so it really does not
> > matter if a switch between the endpoint and the root port supports ACS
> > if the upstream root port does not.  Packets could be rerouted at the
> > root port regardless of how much isolation exists downstream of it.  
> Well shoot, I obviously hadn't grasped that. ;(
> >> If anyone has followed my rambling this far, thank you for your extreme
> >> patience.  I would like to thank Alex Williamson for his vfio blog and
> >> the kvmforum talk up on youtube -- I would be completely lost at this
> >> point without that information.  
> > Thanks!  I certainly discourage use of the ACS override patch, which
> > at least for my part is why you don't see forward ports of it.  AFAIK,
> > it's not possible to get separate IOMMU groups for the processor root
> > ports on i3/5/7/E3 otherwise though.  If you need to stick with this
> > product family, you'll need to figure out how to make a configuration
> > where the processor root ports are used exclusively by either the host
> > or the guest.  We do have ACS equivalent isolation in the PCH root
> > ports, but of course that moves you further from the CPU and might
> > restrict full bandwidth.  Otherwise you need a Xeon E5 or High End
> > Desktop processor.  As I document in my setup, I use IGD for host
> > graphics and can therefore dedicate the processor root port to the
> > guest graphics.  I can use the PCH root ports for a 3rd guest if
> > necessary.  
> I don't believe there is an IGD configuration that would work for me as
> I need to drive 3x 1920x1200 displays.  The displays I have (total of 6)
> are all DP1.2, which means I need at least least 1 MST capable DP +
> another port (DP1.2 doesn't have enough bandwidth for 3 displays at that
> resolution).  I had an issue with monitors randomly not going into
> powersave when daisy chained via MST and have switched to using 3 fully
> independent DPs.
> 
> Do you know if all E5s have ACS on the root port -- including the low
> end E5-1600v4 family?

The same data sheet covers the E5-4600, 2600, and 1600 processors and
indicates ACS support.  Unless I've missed a footnote somewhere, I'd
think that means even the low end E5s have ACS.  Thanks,

Alex