CPU Throttling - CI/CD Glossary Definition
CPU throttling is when the kernel (via cgroups CFS quota) caps a container or process to its allotted CPU share, pausing it once it has used its quota within a scheduling period. The process is runnable but forcibly stopped, which shows up as slow execution despite low average CPU.
Why CI jobs hit it
A container with a CPU limit of 1 core that tries to use 4 during a burst gets throttled, stretching wall-clock time even though plenty of host CPU is idle. On Linux, cat /sys/fs/cgroup/cpu.stat shows nr_throttled and throttled_usec. Raising or removing the CPU limit, or running on a runner sized for the workload, resolves it.
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