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MrDuk
Asked: 2016-08-10 11:22:05 +0800 CST

How does process CPU usage relate to Load Average? [duplicate]

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I have the following host / load:

  • Two 6-core CPUs, with HT (From what I understand, max load would be 24.0)
  • 12 "primary" processes, with sustained usage of about 50% CPU
  • Load average: 0.86 0.98 0.98

Could someone help me understand:

  • How do multiple processes have sustained load, while the Load Average of the box is seemingly low? Considering 12 cores at 50%, I'd expect the load to at least hit somewhere between 6.0 - 12.0.
  • Considering CPU usage alone, are there any low-level details preventing me from adding more services to this host until the Load average hits ~24? (not concerned about disk I/O, memory, or anything else for the sake of this question -- I just want to fully understand how reliable the Load average is when considering CPU bottle-necking; thread waiting? bus contention? anything that's not represented in the Load average concerning CPU use?)
centos unix cpu-usage load-average

1 Answers

  1. Load is not the number of processes currently running on CPU, but the number waiting for CPU time. So if you have, say, 8 cores then 8 threads can use a full core each without the load being affected. (This is not a likely scenario as there are much more threads.)

    Also, the only upper limit for the load is the number of processes that can run simultaneously on a system. I've seen values of 100 and more.

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