On 12/1/2021 2:44 PM, Thomas Gleixner wrote:
On Wed, Dec 01 2021 at 14:21, Dave Jiang wrote:
On 12/1/2021 1:25 PM, Thomas Gleixner wrote:
The hardware implementation does not have enough MSIX vectors for
guests. There are only 9 MSIX vectors total (8 for queues) and 2048 IMS
vectors. So if we are to do MSI-X for all of them, then we need to do
the IMS backed MSIX scheme rather than passthrough IMS to guests.
Confused. Are you talking about passing a full IDXD device to the guest
or about passing a carved out subdevice, aka. queue?
I'm talking about carving out a subdevice. I had the impression of you
wanting IMS passed through for all variations. But it sounds like for a
sub-device, you are ok with the implementation of MSIX backed by IMS?
I don't see anything wrong with that. A subdevice is it's own entity and
VFIO can chose the most conveniant representation of it to the guest
obviously.
How that is backed on the host does not really matter. You can expose
MSI-X to the guest with a INTx backing as well.
I'm still failing to see the connection between the 9 MSIX vectors and
the 2048 IMS vectors which I assume that this is the limitation of the
physical device, right?
I think I was confused with what you were asking and was thinking you
are saying why can't we just have MSIX on guest backed by the MSIX on
the physical device and thought there would not be enough vectors to
service the many guests. I think I understand what your position is now
with the clarification above.
What needs a subdevice to expose?
Thanks,
tglx
