CPU time is the amount of time that a program or application spends for processing instructions on a central processing unit (CPU). CPU time is measured in seconds, and represents the actual computational workload used by the CPU to execute a program. Its a subset of the overall execution time, or wall time, which also includes time spent waiting for input/output (I/O) operations, idle time, and time spent on initializing and terminating the program.
CPU time is a useful metric for measuring performance, as it provides an indication of the amount of computational work that is being done. It is often used to compare the efficiency of different algorithms or implementations of a program, and to identify areas where optimization may be needed.
CPU time is a key variable in computing usage charges in cloud computing environments, where it is used to calculate the cost of running a program or application on a virtual machine or cloud service. For example, Cloudflare uses CPU time as a metric for billing customers for the amount of computational resources used by their applications running on Cloudflare Workers, and provides tools for monitoring and optimizing CPU time usage.
Cloudflare’s use of CPU time as a billing metric makes it a cost-effective option for running serverless applications, as it allows customers to pay only for the computational resources they actually use, rather than for the capacity of the virtual machine or cloud service.
Other cloud computing providers, such as AWS, charge based on the wall time, not the CPU time. Thats the case of AWS Lambda, where the billing is primarily based on the number of requests and the wall time or total duration of the function execution.