Performance Counters in HPX are used to provide information as to how well the runtime system or an application is performing. The counter data can help determine system bottlenecks and fine-tune system and application performance. The HPX runtime system, its networking, and other layers provide counter data that an application can consume to provide users with information of how well the application is performing.

Applications can also use counter data to determine how much system resources to consume. For example, an application that transfers data over the network could consume counter data from a network switch to determine how much data to transfer without competing for network bandwidth with other network traffic. The application could use the counter data to adjust its transfer rate as the bandwidth usage from other network traffic increases or decreases.

Performance Counters are HPX parallel processes which expose a predefined interface. HPX exposes special API functions that allow one to create, manage, read the counter data, and release instances of Performance Counters. Performance Counter instances are accesssed by name, and these names have a predefined structure which is described in the section Performance Counter Names. The advantage of this is that any Performance Counter can be accessed remotely (from a different locality) or locally (from the same locality). Moreover, since all counters expose their data using the same API, any code consuming counter data can be utilized to access arbitrary system information with minimal effort.

Counter data may be accesssed in real time. More information about how to consume counter data can be found in the section Consuming Performance Counters.

All HPX applications provide command line options related to performance counters, such as the ability to list available counter types, or periodically query specific counters to be printed to the screen or save them in a file. For more information, please refer to the section HPX Command Line Options.