I guess I should clarify that my point was purely in abstract and not specific to the XBox situation.
Of course in reality it depends on the hypervisor and the deployed configuration. Running a database under an ESXi VM with SSDs connected to a passed-through PCIe controller (under x86_64 with hardware-assisted CPU and IO virtualization enabled and correctly activated, interrupts working correctly, etc) gives me performance numbers within the statistical error margin when compared to the same configuration without ESXi in the picture.
I haven’t quantified the GPU performance similarly but others have and the performance hit (again, under different hypervisors) is definitely not what you make it out to be.
My point was that if there’s a specific performance hit, it would be pedantically incorrect to say “virtualizing the GPU is the problem” as compared to saying “the way MS virtualized GPU access caused a noticeable drop in achievable graphics.”
Sorry, I don't think I implied virtualising the GPU is the problem.
I said "the fact that it's a VM has caused performance degradation enough that graphical fidelity was diminished" - this is an important distinction.
To clarify further: the GPU and CPU is a unified package and the request pipeline is also shared, working overtime to send things to RAM will affect GPU bandwidth, so overhead of memory allocations that are non-GPU will still affect the GPU due to that limited bandwidth being used.
I never checked if the GPU bandwidth was constrained by the hypervisor to be fair, because such a thing was not possible to test, the only corrolary is the PS4 which we didn't optimise as much as we did for DX and ran on slightly less performant hardware.
Of course in reality it depends on the hypervisor and the deployed configuration. Running a database under an ESXi VM with SSDs connected to a passed-through PCIe controller (under x86_64 with hardware-assisted CPU and IO virtualization enabled and correctly activated, interrupts working correctly, etc) gives me performance numbers within the statistical error margin when compared to the same configuration without ESXi in the picture.
I haven’t quantified the GPU performance similarly but others have and the performance hit (again, under different hypervisors) is definitely not what you make it out to be.
My point was that if there’s a specific performance hit, it would be pedantically incorrect to say “virtualizing the GPU is the problem” as compared to saying “the way MS virtualized GPU access caused a noticeable drop in achievable graphics.”