Safe Haskell	None
Language	Haskell2010

Vulkan.Extensions.VK_KHR_global_priority

Description

Name

VK_KHR_global_priority - device extension

VK_KHR_global_priority

Name String: VK_KHR_global_priority

Extension Type

Device extension

Registered Extension Number

189

Revision

1

Ratification Status

Ratified

Extension and Version Dependencies

VK_KHR_get_physical_device_properties2 or Vulkan Version 1.1

Deprecation State

Promoted to Vulkan 1.4

Contact

Tobias Hector @tobski%0A*Here describe the issue or question you have about the VK_KHR_global_priority extension*

Other Extension Metadata

Last Modified Date: 2021-10-22

Contributors

Tobias Hector, AMD
Contributors to VK_EXT_global_priority
Contributors to VK_EXT_global_priority_query

Description

In Vulkan, users can specify device-scope queue priorities. In some cases it may be useful to extend this concept to a system-wide scope. This device extension allows applications to query the global queue priorities supported by a queue family, and then set a priority when creating queues. The default queue priority is QUEUE_GLOBAL_PRIORITY_MEDIUM_EXT.

Implementations can report which global priority levels are treated differently by the implementation. It is intended primarily for use in system integration along with certain platform-specific priority enforcement rules.

The driver implementation will attempt to skew hardware resource allocation in favor of the higher-priority task. Therefore, higher-priority work may retain similar latency and throughput characteristics even if the system is congested with lower priority work.

The global priority level of a queue shall take precedence over the per-process queue priority (DeviceQueueCreateInfo::pQueuePriorities).

Abuse of this feature may result in starving the rest of the system from hardware resources. Therefore, the driver implementation may deny requests to acquire a priority above the default priority (QUEUE_GLOBAL_PRIORITY_MEDIUM_EXT) if the caller does not have sufficient privileges. In this scenario ERROR_NOT_PERMITTED_EXT is returned.

The driver implementation may fail the queue allocation request if resources required to complete the operation have been exhausted (either by the same process or a different process). In this scenario ERROR_INITIALIZATION_FAILED is returned.

New Structures

Extending DeviceQueueCreateInfo:
- DeviceQueueGlobalPriorityCreateInfoKHR

Extending PhysicalDeviceFeatures2, DeviceCreateInfo:
- PhysicalDeviceGlobalPriorityQueryFeaturesKHR
Extending QueueFamilyProperties2:
- QueueFamilyGlobalPriorityPropertiesKHR

New Enums

QueueGlobalPriorityKHR

New Enum Constants

KHR_GLOBAL_PRIORITY_EXTENSION_NAME

Promotion to Vulkan 1.4

Functionality in this extension is included in core Vulkan 1.4 with the KHR suffix omitted. The original type, enum, and command names are still available as aliases of the core functionality.

Issues

1) Can we additionally query whether a caller is permitted to acquire a specific global queue priority in this extension?

RESOLVED: No. Whether a caller has enough privilege goes with the OS, and the Vulkan driver cannot really guarantee that the privilege will not change in between this query and the actual queue creation call.

2) If more than 1 queue using global priority is requested, is there a good way to know which queue is failing the device creation?

RESOLVED: No. There is not a good way at this moment, and it is also not quite actionable for the applications to know that because the information may not be accurate. Queue creation can fail because of runtime constraints like insufficient privilege or lack of resource, and the failure is not necessarily tied to that particular queue configuration requested.