include::meta/VK_EXT_global_priority.txt[]

*Last Modified Date*::
     2017-10-06
*IP Status*::
    No known IP claims.
*Contributors*::
  - Andres Rodriguez, Valve
  - Pierre-Loup Griffais, Valve
  - Dan Ginsburg, Valve
  - Mitch Singer, AMD

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 extension provides a mechanism for caller's to set their system-wide
priority.
The default queue priority is ename:VK_QUEUE_GLOBAL_PRIORITY_MEDIUM_EXT.

The driver implementation will attempt to skew hardware resource allocation
in favour 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 predence over the
per-process queue priority
(sname:VkDeviceQueueCreateInfo::pname: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 (ename:VK_QUEUE_GLOBAL_PRIORITY_MEDIUM_EXT) if
the caller does not have sufficient privileges.
In this scenario ename:VK_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 ename:VK_ERROR_INITIALIZATION_FAILED is returned.

=== New Object Types

None.

=== New Enum Constants

  * Extending elink:VkStructureType:
  ** ename:VK_STRUCTURE_TYPE_DEVICE_QUEUE_GLOBAL_PRIORITY_CREATE_INFO_EXT

  * Extending elink:VkResult:
  ** ename:VK_ERROR_NOT_PERMITTED_EXT

=== New Enums

  * elink:VkQueueGlobalPriorityEXT

=== New Structures

  * slink:VkDeviceQueueGlobalPriorityCreateInfoEXT

=== New Functions

None.

=== Issues

None.

=== Version History

 * Revision 2, 2017-11-03 (Andres Rodriguez)
   - Fixed VkQueueGlobalPriorityEXT missing _EXT suffix

 * Revision 1, 2017-10-06 (Andres Rodriguez)
   - First version.