Performance Hints and Thread Scheduling#

To simplify the configuration of hardware devices, it is recommended to use the ov::hint::PerformanceMode::LATENCY and ov::hint::PerformanceMode::THROUGHPUT high-level performance hints. Both performance hints ensure optimal portability and scalability of applications across various platforms and models.

  • ov::inference_num_threads limits the number of logical processors used for CPU inference. If the number set by the user is greater than the number of logical processors on the platform, the multi-threading scheduler only uses the platform number for CPU inference.

  • ov::num_streams limits the number of infer requests that can be run in parallel. If the number set by the user is greater than the number of inference threads, multi-threading scheduler only uses the number of inference threads to ensure that there is at least one thread per stream.

  • ov::hint::scheduling_core_type specifies the type of CPU cores for CPU inference when the user runs inference on a hybird platform that includes both Performance-cores (P-cores) and Efficient-cores (E-cores). If the user platform only has one type of CPU core, this property has no effect, and CPU inference always uses this unique core type.

  • ov::hint::enable_hyper_threading limits the use of one or two logical processors per CPU core when the platform has CPU hyperthreading enabled. If there is only one logical processor per CPU core, such as Efficient-cores, this property has no effect, and CPU inference uses all logical processors.

  • ov::hint::enable_cpu_pinning enables CPU pinning during CPU inference. If the user enables this property but the inference scenario does not support it, this property will be disabled during model compilation.

For additional details on the above configurations, refer to Multi-stream Execution.

Latency Hint#

In this scenario, the default setting of ov::hint::scheduling_core_type is determined by the model precision and the ratio of P-cores and E-cores.

Note

P-cores is short for Performance-cores and E-cores stands for Efficient-cores. These types of cores are available starting with the 12th Gen Intel® Core™ processors.

INT8 Model

FP32 Model

E-cores / P-cores < 2

P-cores

P-cores

2 <= E-cores / P-cores < 4

P-cores

P-cores and E-cores

4 <= E-cores / P-cores

P-cores and E-cores

P-cores and E-cores

Note

Both P-cores and E-cores may be used for any configuration starting with 14th Gen Intel® Core™ processors on Windows.

Then the default settings for low-level performance properties on Windows and Linux are as follows:

Property

Windows

Linux

ov::num_streams

1

1

ov::inference_num_threads

is equal to the number of P-cores or P-cores+E-cores on one socket

is equal to the number of P-cores or P-cores+E-cores on one socket

ov::hint::scheduling_core_type

Core Type Table of Latency Hint

Core Type Table of Latency Hint

ov::hint::enable_hyper_threading

No

No

ov::hint::enable_cpu_pinning

No / Not Supported

Yes except using P-cores and E-cores together

Note

  • ov::hint::scheduling_core_type may be adjusted for a particular inferred model on a specific platform based on internal heuristics to guarantee optimal performance.

  • Both P-cores and E-cores are used for the Latency Hint on Intel® Core™ Ultra Processors on Windows, except in the case of large language models.

  • In case hyper-threading is enabled, two logical processors share the hardware resources of one CPU core. OpenVINO does not expect to use both logical processors in one stream for a single infer request. So ov::hint::enable_hyper_threading is set to No in this scenario.

  • ov::hint::enable_cpu_pinning is disabled by default on Windows and macOS, and enabled on Linux. Such default settings are aligned with typical workloads running in the corresponding environments to guarantee better out-of-the-box (OOB) performance.

Throughput Hint#

In this scenario, thread scheduling first evaluates the memory pressure of the model being inferred on the current platform, and determines the number of threads per stream, as shown below.

Memory Pressure

Threads per Stream

low

1 P-core or 2 E-cores

medium

2

high

3 or 4 or 5

Then the value of ov::num_streams is calculated by dividing ov::inference_num_threads by the number of threads per stream. The default settings for low-level performance properties on Windows and Linux are as follows:

Property

Windows

Linux

ov::num_streams

Calculated as above

Calculated as above

ov::inference_num_threads

Number of P-cores and E-cores

Number of P-cores and E-cores

ov::hint::scheduling_core_type

P-cores and E-cores

P-cores and E-cores

ov::hint::enable_hyper_threading

Yes / No

Yes / No

ov::hint::enable_cpu_pinning

No

Yes

Note

By default, different core types are not mixed within a single stream in this scenario. The cores from different NUMA nodes are not mixed within a single stream.

Multi-Threading Optimization#

The following properties can be used to limit the available CPU resources for model inference. If the platform or operating system supports this behavior, the OpenVINO Runtime will perform multi-threading scheduling based on the limited available CPU.

  • ov::inference_num_threads

  • ov::hint::scheduling_core_type

  • ov::hint::enable_hyper_threading

# Use one logical processor for inference
compiled_model_1 = core.compile_model(
    model=model,
    device_name=device_name,
    config={properties.inference_num_threads(): 1},
)

# Use logical processors of Efficient-cores for inference on hybrid platform
compiled_model_2 = core.compile_model(
    model=model,
    device_name=device_name,
    config={
        properties.hint.scheduling_core_type(): properties.hint.SchedulingCoreType.ECORE_ONLY,
    },
)

# Use one logical processor per CPU core for inference when hyper threading is on
compiled_model_3 = core.compile_model(
    model=model,
    device_name=device_name,
    config={properties.hint.enable_hyper_threading(): False},
)
        // Use one logical processor for inference
        auto compiled_model_1 = core.compile_model(model, device, ov::inference_num_threads(1));

        // Use logical processors of Efficient-cores for inference on hybrid platform
        auto compiled_model_2 = core.compile_model(model, device, ov::hint::scheduling_core_type(ECORE_ONLY));

        // Use one logical processor per CPU core for inference when hyper threading is on
        auto compiled_model_3 = core.compile_model(model, device, ov::hint::enable_hyper_threading(false));

Note

ov::hint::scheduling_core_type and ov::hint::enable_hyper_threading only support Intel® x86-64 CPU on Linux and Windows in the current release.

In some use cases, OpenVINO Runtime will enable CPU thread pinning by default for better performance. Users can also turn this feature on or off using the property ov::hint::enable_cpu_pinning. Disabling thread pinning may be beneficial in complex applications where several workloads are executed in parallel.

# Disable CPU thread pinning for inference when the system supports it
compiled_model_4 = core.compile_model(
    model=model,
    device_name=device_name,
    config={properties.hint.enable_cpu_pinning(): False},
)
        // Disable CPU threads pinning for inference when system support it
        auto compiled_model_4 = core.compile_model(model, device, ov::hint::enable_cpu_pinning(false));

For details on multi-stream execution check the optimization guide.