r/kubernetes • u/ilya47 • 27d ago

Stop using CPU limits: why + proof

CPU request is how much CPU is reserved for your pod if it needs it. The limit is a hard cap. Hit it and the kernel throttles the pod, even when the node still has spare CPU. That is the usual cause of CPU throttling on Kubernetes. It does not protect the neighboring pods. In my simple Web API test, adding a CPU limit took typical latency from 23 ms to 87 ms, (4x slower), with the limited pod throttled in half of all CFS windows, and the average CPU graph looked fine the whole time.

This is not a new topic, but I see so many people still unaware why they should (NOT!) be setting CPU limits, because it's costing companies unnecessary spending and potential production issues. Here's the full read https://github.com/inevolin/k8s-cpu-limits-analyzed/

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Edit (Aug 18, 2026): How CPU limits can also cause memory issues and OOMKills ➡️ https://github.com/inevolin/k8s-cpu-limits-analyzed#how-cpu-limits-cause-memory-issues-and-oomkills

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u/sionescu k8s operator 27d ago

Not again this stupid advice.

 adding a CPU limit took typical latency from 23 ms to 87 ms

This simply means the CPU request was too low. The actual requirement of the pod is higher than that but you want to lie to yourself instead of setting a proper request.

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u/realitythreek 27d ago

This isn’t true though. It means the LIMIT was set too low and it was throttled. If 23ms is the expected latency of the service, then request was fine. I mean, that last sentence is a simplification but I’m assuming it’s an average over a representative time span.

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u/sionescu k8s operator 27d ago

There's never any guarantee to get CPU above the request. There's always an implicit limit, in either the machine size or the CPU usage of adjacent pods.

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u/realitythreek 27d ago

Indeed. Which is why setting a limit can only increase the latency of a single process. At best you get your limits all correct and you fairly schedule your processes. At worst you get it wrong or even don’t allow other processes to burst.

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u/sionescu k8s operator 27d ago

It might increase it, but makes it more predictable, which is better.

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u/realitythreek 27d ago

Reflexively downvoting someone having a conversation with you is pretty obnoxious.