Environment variables

Behavior of dpctl is affected by environment variables that affect DPC++ compiler runtime. Other relevant environment variables that may not be documented here can be found in:

• Level Zero

• OneAPI

Variable ONEAPI_DEVICE_SELECTOR

The variable ONEAPI_DEVICE_SELECTOR can be used to limit the choice of devices available to dpctl. Please refer to Managing Devices for detailed description and uses.

Variable SYCL_PI_TRACE

Setting this debugging variable enables specific levels of tracing for SYCL Programming Interfaces (PI). The value of the variable is a bit-mask, with the following supported values:

Value	Description
1	Enables tracing of PI plugins/devices discovery
2	Enables tracing of PI calls
-1	Enables all levels of tracing

Variable ZE_FLAT_DEVICE_HIERARCHY

Allows users to define the device hierarchy model exposed by Level Zero driver implementation. Keep in mind dpctl.get_composite_devices will only work while this is set to COMBINED.

Value	Description
COMBINED	Level Zero devices with multiple tiles will be exposed as a set of root devices, each corresponding to an individual tile. These root devices are component devices, which can be queried for their corresponding composite device, and the composite device can in turn be queried for components. Dedicated composite device APIs will return non-trivial results.
COMPOSITE	Level Zero devices with multiple tiles will be exposed as a singular root device, with tiles accessible as sub-devices.
FLAT	Level Zero devices with multiple tiles will be exposed as a set of root devices, each corresponding to an individual tile. Enabled by default.

Read more about device hierarchy in Level Zero Specification and Intel GPU article.

Variable ZE_AFFINITY_MASK

Allows users to mask specific devices from being used by SYCL applications. If we have ZE_FLAT_DEVICE_HIERARCHY set to COMPOSITE, we can have an AFFINITY of “1” for our application to only see device #1 - making system devices 0, and 2+, invisible.

If we have ZE_FLAT_DEVICE_HIERARCHY set to FLAT, we can have a ZE_AFFINITY_MASK of “1” for our application to only see the second tile in the system as logical device #0. If the system has four dual-tile GPUs installed, this would be the second tile in the first GPU. In FLAT mode, the numbers use a system-wide-sub-device-number from a flat numbering perspective. Therefore, we could use the second tile in each of four dual-tile GPUs with ZE_AFFINITY_MASK=1,3,5,7.

If we have ZE_FLAT_DEVICE_HIERARCHY set to COMBINED, the way tiles and composite devices are exposed depends on the physical devices present and the value of ZE_AFFINITY_MASK:

If all exposed tiles (as determined by ``ZE_AFFINITY_MASK``) belong to the same physical device:

- That composite device is available to the application, and each tile is accessible as a component device of that composite device.

If the exposed tiles belong to different physical devices:

- A composite device is available for each physical device, and the tiles are accessible as component devices of their respective composite device.

Additional examples to illustrate this are in the detailed documentation for ZE_AFFINITY_MASK, read more about it in Level Zero Specification.

Variable ZE_ENABLE_PCI_ID_DEVICE_ORDER

Forces driver to report devices from lowest to highest PCI bus ID.

Value	Description
0	Disabled. Default value.
1	Enabled.

Variable ZE_SHARED_FORCE_DEVICE_ALLOC

Forces all shared allocations into device memory

Value	Description
0	Disabled. Default value.
1	Enabled.