Device Groups and Logical Device

bryanmcconkey · April 2, 2018, 11:15am

Feel free to point me to the correct spot if this is outlined somewhere and I simply missed it. I could not find my answer searching in the specification.

My question is in regards to creating a logical device with more than 1 physical device withVkDeviceGroupDeviceCreateInfo.
How does that impact queue families, extensions, and other things that are physical device specific?
Will a device group only ever exist when these things match exactly? Or are the limits of the physical device referenced directly in VkDeviceCreateInfo the only ones that matter?

I’d love to write something that will take advantage of this when possible, but I can not seem to find details on the specifics of how it impacts the supported queues and extensions etc.

Thanks in advance!

Bryan

krOoze · April 3, 2018, 8:12am

In all likelihood the physical devices in a group will be identical.

I would say vkCreateDevice::physicalDevice still determines all that. But you better make an Issue.

bryanmcconkey · April 4, 2018, 5:59am

Thanks krOoze, I agree with your assumption that they probably only ever will match exactly, but I don’t like to make assumptions.

I have filed an issue to have this explicitly defined in the spec:

github.com/KhronosGroup/Vulkan-Docs

Device Limits When Using VkDeviceGroupDeviceCreateInfo

opened 12:57PM - 04 Apr 18 UTC

closed 01:04PM - 24 May 19 UTC

bryanmcconkey

Resolving Inside Khronos

The specification does not outline how queue families, extensions, and other thi…ngs that are physical device specific impact creation of a logical device when using VkDeviceGroupDeviceCreateInfo with a device group. I would *think* that it must be one of two things. A) A device group will only ever exist when these limits match exactly (ie same physical card x 2 etc) B) The limits of the physical device referenced directly by the vkCreateDevice structure are the ones that matter, the drivers would take care any physical device differences among the device group. I feel like A is the most likely, but I do not actually know, and feel the specification should be explicit about what device limits one can expect when using device groups. Thanks!