# Query Device Properties - Configuration {#openvino_docs_OV_UG_query_api}


The OpenVINO™ toolkit supports inference with several types of devices (processors or accelerators).
This section provides a high-level description of the process of querying of different device properties and configuration values at runtime.

OpenVINO runtime has two types of properties:
- Read only properties which provide information about the devices (such as device name, thermal state, execution capabilities, etc.) and information about configuration values used to compile the model (`ov::CompiledModel`) .
- Mutable properties which are primarily used to configure the `ov::Core::compile_model` process and affect final inference on a specific set of devices. Such properties can be set globally per device via `ov::Core::set_property` or locally for particular model in the `ov::Core::compile_model` and the `ov::Core::query_model` calls.

An OpenVINO property is represented as a named constexpr variable with a given string name and a type. The following example represents a read-only property with a C++ name of `ov::available_devices`, a string name of `AVAILABLE_DEVICES` and a type of `std::vector<std::string>`:
```
static constexpr Property<std::vector<std::string>, PropertyMutability::RO> available_devices{"AVAILABLE_DEVICES"};
```

Refer to the [Hello Query Device С++ Sample](../../../samples/cpp/hello_query_device/README.md) sources and the [Multi-Device execution](../multi_device.md) documentation for examples of using setting and getting properties in user applications.

### Get a Set of Available Devices

Based on the `ov::available_devices` read-only property, OpenVINO Core collects information about currently available devices enabled by OpenVINO plugins and returns information, using the `ov::Core::get_available_devices` method:

@sphinxtabset

@sphinxtab{C++}

@snippet docs/snippets/ov_properties_api.cpp get_available_devices

@endsphinxtab

@sphinxtab{Python}

@snippet docs/snippets/ov_properties_api.py get_available_devices

@endsphinxtab

@endsphinxtabset


The function returns a list of available devices, for example:

```
MYRIAD.1.2-ma2480
MYRIAD.1.4-ma2480
CPU
GPU.0
GPU.1
```

If there are multiple instances of a specific device, the devices are enumerated with a suffix comprising a full stop and a unique string identifier, such as `.suffix`. Each device name can then be passed to:

* `ov::Core::compile_model` to load the model to a specific device with specific configuration properties.
* `ov::Core::get_property` to get common or device-specific properties.
* All other methods of the `ov::Core` class that accept `deviceName`.

### Working with Properties in Your Code

The `ov::Core` class provides the following method to query device information, set or get different device configuration properties:

* `ov::Core::get_property` - Gets the current value of a specific property.
* `ov::Core::set_property` - Sets a new value for the property globally for specified `device_name`.

The `ov::CompiledModel` class is also extended to support the properties:

* `ov::CompiledModel::get_property`
* `ov::CompiledModel::set_property`

For documentation about OpenVINO common device-independent properties, refer to the `openvino/runtime/properties.hpp`. Device-specific configuration keys can be found in corresponding device folders (for example, `openvino/runtime/intel_gpu/properties.hpp`).

### Working with Properties via Core

#### Getting Device Properties

The code below demonstrates how to query `HETERO` device priority of devices which will be used to infer the model:

@sphinxtabset

@sphinxtab{C++}

@snippet docs/snippets/ov_properties_api.cpp hetero_priorities

@endsphinxtab

@sphinxtab{Python}

@snippet docs/snippets/ov_properties_api.py hetero_priorities

@endsphinxtab

@endsphinxtabset

> **NOTE**: All properties have a type, which is specified during property declaration. Based on this, actual type under `auto` is automatically deduced by C++ compiler.

To extract device properties such as available devices (`ov::available_devices`), device name (`ov::device::full_name`), supported properties (`ov::supported_properties`), and others, use the `ov::Core::get_property` method:

@sphinxtabset

@sphinxtab{C++}

@snippet docs/snippets/ov_properties_api.cpp cpu_device_name

@endsphinxtab

@sphinxtab{Python}

@snippet docs/snippets/ov_properties_api.py cpu_device_name

@endsphinxtab

@endsphinxtabset

A returned value appears as follows: `Intel(R) Core(TM) i7-8700 CPU @ 3.20GHz`.

> **NOTE**: In order to understand a list of supported properties on `ov::Core` or `ov::CompiledModel` levels, use `ov::supported_properties` which contains a vector of supported property names. Properties which can be changed, has `ov::PropertyName::is_mutable` returning the `true` value. Most of the properites which are changable on `ov::Core` level, cannot be changed once the model is compiled, so it becomes immutable read-only property.

#### Configure a Work with a Model

The `ov::Core` methods like:

* `ov::Core::compile_model`
* `ov::Core::import_model`
* `ov::Core::query_model`

accept a selection of properties as last arguments. Each of the properties should be used as a function call to pass a property value with a specified property type.

@sphinxtabset

@sphinxtab{C++}

@snippet docs/snippets/ov_properties_api.cpp compile_model_with_property

@endsphinxtab

@sphinxtab{Python}

@snippet  docs/snippets/ov_properties_api.py compile_model_with_property

@endsphinxtab

@endsphinxtabset

The example below specifies hints that a model should be compiled to be inferred with multiple inference requests in parallel to achieve best throughput, while inference should be performed without accuracy loss with FP32 precision.

#### Setting Properties Globally

`ov::Core::set_property` with a given device name should be used to set global configuration properties, which are the same across multiple `ov::Core::compile_model`, `ov::Core::query_model`, and other calls. However, setting properties on a specific `ov::Core::compile_model` call applies properties only for the current call:

@sphinxtabset

@sphinxtab{C++}

@snippet docs/snippets/ov_properties_api.cpp core_set_property_then_compile

@endsphinxtab

@sphinxtab{Python}

@snippet  docs/snippets/ov_properties_api.py core_set_property_then_compile

@endsphinxtab

@endsphinxtabset

### Properties on CompiledModel Level

#### Getting Property

The `ov::CompiledModel::get_property` method is used to get property values the compiled model has been created with or a compiled model level property such as `ov::optimal_number_of_infer_requests`:

@sphinxtabset

@sphinxtab{C++}

@snippet docs/snippets/ov_properties_api.cpp optimal_number_of_infer_requests

@endsphinxtab

@sphinxtab{Python}

@snippet  docs/snippets/ov_properties_api.py optimal_number_of_infer_requests

@endsphinxtab

@endsphinxtabset

Or the current temperature of the `MYRIAD` device:

@sphinxtabset

@sphinxtab{C++}

@snippet docs/snippets/ov_properties_api.cpp device_thermal

@endsphinxtab

@sphinxtab{Python}

@snippet  docs/snippets/ov_properties_api.py device_thermal

@endsphinxtab

@endsphinxtabset


Or the number of threads that would be used for inference on `CPU` device:

@sphinxtabset

@sphinxtab{C++}

@snippet docs/snippets/ov_properties_api.cpp inference_num_threads

@endsphinxtab

@sphinxtab{Python}

@snippet  docs/snippets/ov_properties_api.py inference_num_threads

@endsphinxtab

@endsphinxtabset

#### Setting Properties for Compiled Model

The only mode that supports this method is [Multi-Device execution](../multi_device.md):

@sphinxtabset

@sphinxtab{C++}

@snippet docs/snippets/ov_properties_api.cpp multi_device

@endsphinxtab

@sphinxtab{Python}

@snippet  docs/snippets/ov_properties_api.py multi_device

@endsphinxtab

@endsphinxtabset