%CPU utilization is a lie

8 days ago

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CPU utilization doesn't increase linearly, making it hard to gauge server limits accurately.
Stress tests on a Ryzen 9 5900X show that at 50% reported CPU utilization, actual work done is 60-100% of max capacity, depending on the task.
Hyperthreading and Turbo Boost significantly affect CPU performance and reported utilization.
Hyperthreading causes performance changes at 50% utilization due to shared resources among cores.
Turbo Boost reduces clock speed as more cores become active, affecting CPU utilization calculations.
Reported CPU utilization can be a significant underestimate when the CPU is used efficiently.
Performance varies between processors, especially between AMD and Intel, due to differences in hyperthreading and Turbo behavior.
The best practice is to benchmark actual work done and compare it to maximum capacity rather than relying on CPU utilization metrics.

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