# Query device properties, configuration {#openvino_docs_OV_UG_query_api}

## Query device properties and devices configuration

The OpenVINO™ toolkit supports inferencing 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 provides information about the devices (such device name, termal, execution capabilities, etc) and information about ov::CompiledModel to understand what configuration values were used to compile the model with.
- Mutable properties which are primarily used to configure ov::Core::compile_model process and affect final inference on the specific set of devices. Such properties can be set globally per device via ov::Core::set_property or locally for particular model in ov::Core::compile_model and ov::Core::query_model calls.

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

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 read-only property `ov::available_devices`, 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 more than one instance of a specific device, the devices are enumerated with `.suffix` where `suffix` is a unique string identifier. 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 `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:

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@sphinxtab{C++}

@snippet docs/snippets/ov_properties_api.cpp hetero_priorities

@endsphinxtab

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@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

`ov::Core` methods like:

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

accept variadic list of properties as last arguments. Each property in such parameters lists should be used as function call to pass property value with 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 inferenced with multiple inference requests in parallel to achive 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 accross multiple `ov::Core::compile_model`, `ov::Core::query_model`, etc. calls, while setting property on the specific `ov::Core::compile_model` call applies properties only for 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`:

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@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:

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@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:

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@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