What does "don't excessively rely on PCIe Resizeable BAR" mean?
Resizable BAR is like 10 years overdue. The idea that you need to go through a driver path to get access to the whole of shared memory is absurd. Why is it excessive to expect the BIOS to set the BAR to cover the whole shared region and leave that small-BAR nonsense in the pa…
What does "don't excessively rely on PCIe Resizeable BAR" mean?
Resizable BAR is like 10 years overdue. The idea that you need to go through a driver path to get access to the whole of shared memory is absurd. Why is it excessive to expect the BIOS to set the BAR to cover the whole shared region and leave that small-BAR nonsense in the past?
What BAR size did you use for your testing? Did a large BAR change the CPU dependency?
I think it's more complicated than that. Sure, resizeable BAR has been in the spec for a very long time, but it wasn't a big deal in the consumer space until AMD pushed it with RDNA 2 in 2021. Even then, you didn't lose a lot of performance if your platform couldn't support resizeable BAR. The same applies to Nvidia's RTX 3000 series. Resizeable BAR on consumer platforms is really a recent thing, only relevant (but not particularly important) to the last couple GPU generations.
Also you can have the GPU copy data from host memory to VRAM, rather than directly having the CPU access VRAM through the BAR range.
I had resizeable BAR working for testing, checked through memory ranges in device manager (the allocated address space is large enough to cover VRAM for both cards)
What does "don't excessively rely on PCIe Resizeable BAR" mean?
Resizable BAR is like 10 years overdue. The idea that you need to go through a driver path to get access to the whole of shared memory is absurd. Why is it excessive to expect the BIOS to set the BAR to cover the whole shared region and leave that small-BAR nonsense in the past?
What BAR size did you use for your testing? Did a large BAR change the CPU dependency?
I think it's more complicated than that. Sure, resizeable BAR has been in the spec for a very long time, but it wasn't a big deal in the consumer space until AMD pushed it with RDNA 2 in 2021. Even then, you didn't lose a lot of performance if your platform couldn't support resizeable BAR. The same applies to Nvidia's RTX 3000 series. Resizeable BAR on consumer platforms is really a recent thing, only relevant (but not particularly important) to the last couple GPU generations.
Also you can have the GPU copy data from host memory to VRAM, rather than directly having the CPU access VRAM through the BAR range.
I had resizeable BAR working for testing, checked through memory ranges in device manager (the allocated address space is large enough to cover VRAM for both cards)