My mac reports 4 Vulkan queue families but reference says it has 1

Question

My home computer is a late 2012 Mac Mini, it has a 3rd gen Intel IvyBridge processor (mobile model for some reason only Apple knows).

The "vulkaninfo.app" from the LunarG SDK reports 4 queue families on the integrated GPU, but public information shows that it should only have 1 one it. What's happening?


VkQueueFamilyProperties[0]:
===========================
    queueFlags         = GRAPHICS | COMPUTE | TRANSFER
    queueCount         = 1
    timestampValidBits = 64
    minImageTransferGranularity = (1, 1, 1)
    present support    = true

VkQueueFamilyProperties[1]:
===========================
    queueFlags         = GRAPHICS | COMPUTE | TRANSFER
    queueCount         = 1
    timestampValidBits = 64
    minImageTransferGranularity = (1, 1, 1)
    present support    = true

VkQueueFamilyProperties[2]:
===========================
    queueFlags         = GRAPHICS | COMPUTE | TRANSFER
    queueCount         = 1
    timestampValidBits = 64
    minImageTransferGranularity = (1, 1, 1)
    present support    = true

VkQueueFamilyProperties[3]:
===========================
    queueFlags         = GRAPHICS | COMPUTE | TRANSFER
    queueCount         = 1
    timestampValidBits = 64
    minImageTransferGranularity = (1, 1, 1)
    present support    = true

Maybe the driver implementation changed? Did you check on that? — Felix K., Jul 21 '19 at 09:47
@FelixK. I did a bit of checking. SDK ver 1.1.108 reports 4 queue families of 1 queue each, 1.0.69 reports 1 queue family of 16 queues. The latter I suspect to be the old MoltonVK driver errornously reporting the number of compute units, which executes in parallel synchronously, unlike queues which executes asynchronously. — DannyNiu, Jul 21 '19 at 10:53

DannyNiu · Accepted Answer · 2019-07-21T12:37:10.543

1

In macOS, there's no queue count or queue family count in Metal Devices (as of July 2019), so one could create 1 or any number of queues and get full utilization of the device.

However, as noted in a GitHub issue, some programs with hardwired assumptions crashes when there's only 1 queue family, so they made MoltenVK report 4 queue families to fix it (see pull request 450).

edited Jul 21 '19 at 12:37

answered Jul 21 '19 at 12:32

DannyNiu

1,313
8
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So, to fix other peoples' broken applications, MoltenVK lies? – Nicol Bolas Jul 21 '19 at 13:32
@NicolBolas basically yes. – DannyNiu Jul 22 '19 at 01:17
3

How do those applications work on Intel implementations, which uniformly expose exactly 1 queue family and exactly 1 queue? – Nicol Bolas Jul 22 '19 at 01:18

My mac reports 4 Vulkan queue families but reference says it has 1

1 Answers1