System information (version)

• OpenCV => 4.1.0
• Operating System / Platform => Ubuntu
• Compiler => g++

Detailed description

OpenCV should have a feature to select the number of CPU cores used for inference when using OpenVINO inference engine as backend.
Right now, this can be only achieved using OpenVINO IE API.

In op_inf_engine.cpp file at
https://github.com/opencv/opencv/blob/master/modules/dnn/src/op_inf_engine.cpp

function

void InfEngineBackendNet::initPlugin(InferenceEngine::ICNNNetwork& net)

can accept the number of CPU cores (num_cores) parameter when DNN_TARGET_CPU is selected.

This can be further passed as

std::map cpu_config<std::string, std::string>
cpu_config[InferenceEngine::PluginConfigParams::KEY_CPU_THREADS_NUM]=std::string(num_cores)
netExec = plugin.LoadNetwork(net, cpu_config);