Low Power Events

Warning

Experimental features:

• May be replaced, updated, or removed at any time.

• Do not require maintaining API/ABI stability of their own additions over time.

• Do not require conformance testing of their own additions.

Motivation

By default, level-zero uses busy polling for waiting on event completion when performing host-based synchronization through APIs such as :ref:`urQueueFinish`. This provides the lowest possible latency for the calling thread, but it may lead to increased CPU utilization.

This extension introduces a new hint flag for :ref:`urQueueCreate`, allowing users to indicate to the runtime that they are willing to sacrifice event completion latency in order to reduce CPU utilization. This may be implemented using interrupt-driven event completion, where the calling thread yields until woken up by the driver.

For applications that want to selectively choose which events should utilize the low-power mode, this extension also adds a new :ref:`urEnqueueEventsWaitWithBarrierExt` function. This enqueue method can be used with an analogous property flag that may cause its output event to be low-power. This barrier is meant to be used on a regular event just before calling synchronization APIs (such as :ref:`urQueueFinish`) to introduce a low-power event.

API

Enums

• ur_device_info_t

  • UR_DEVICE_INFO_LOW_POWER_EVENTS_EXP

• ur_queue_flags_t

  • UR_QUEUE_FLAG_LOW_POWER_EVENTS_EXP

• ur_exp_enqueue_ext_flags_t

  • UR_EXP_ENQUEUE_EXT_FLAG_LOW_POWER_EVENTS

• ur_structure_type_t

  • {X}_STRUCTURE_TYPE_EXP_ENQUEUE_EXT_PROPERTIES

Types

ur_exp_enqueue_ext_properties_t

Functions

• urEnqueueEventsWaitWithBarrierExt

Changelog

Revision	Changes
1.0	Initial Draft

Support

Adapters which support this experimental feature must return true for the new :ref:`UR_DEVICE_INFO_LOW_POWER_EVENTS_EXP <ur-device-info-t>`\ device info query.

Contributors

• Piotr Balcer piotr.balcer@intel.com