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I have a high system load (> 1.5ish), but a low CPU load (> 80% idle), with the fan running on what sounds like overdrive.

The problem is that I can't figure out what is causing the computer to be dragged down because it is apparently an IO issue, not a CPU issue.

Any ideas? I'm running the latest version of lion. This happens fairly frequently as well.

To clarify, the cpu is mostly idle.

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3 Answers

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1.5 is not a high load, especially on a multi-core machine. Fan can be on overdrive because of a faulty temperature sensor or blocked airflow or things like that. Using a laptop in bed and resting it on a down comforter, for example, can send the fan into overdrive. Also, the GPU (video card) can generate more heat than the CPU and won't show up in load metrics at all. Are you doing something graphics intensive, like editing video or playing video games?

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1.5 isn't a high load... but with a CPU that is almost completely idle, it seems a little high. The graphics card being used might be the problem, and would explain some things. – Andrew Spott Apr 25 '12 at 17:34
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Aside from physical issues that Old Pro addressed, it's possible that you're using a program which isn't multithreaded. Mac OS swaps active cores for any given process intermittently, but if the program is queued up for the foreseeable future, it will run as close to 100% as possible. This can cause the CPU die to heat up and the ~1 load. If you're noticing significant disk usage, it's likely that this is the case.

To further diagnose your issue, try using Activity Monitor to see which processes are using the most CPU. You can also diagnose disk usage here.

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The CPU isn't actually anywhere near 100% utilization. it is almost completely idle, but the load is still high. Which is what is bugging me. – Andrew Spott Apr 25 '12 at 17:36
That's 100% for a single thread, which will at most take up a single logical executing path on your CPU. For example, a Core i7 would only be utilizing 1/8th (4 cores * 2 (for hyperthreading) = 8 logical cores) of the available utilization = 12.5%. So no, it's not 100% of total utilization, just a single core's utilization, which is different on each processor type. – zwerdlds Apr 25 '12 at 17:40
top reports CPU as % of one cpu (so 1 cpu working at full cycles is 100%, 2 cpus is 200%, etc) So, actually, 10% utilization is not even close to 1 cpus worth of utilization. – Andrew Spott Apr 25 '12 at 22:51
You're right, top display CPU info using that format. Activity Monitor, on the other hand, uses "100%" = 100% available utilization. Regardless, this doesn't address the issue. Did you identify the process which is exceeding your usage expectations? – zwerdlds Apr 26 '12 at 14:48
unfortunately I haven't, but it is a recurring problem, so I'll have to keep checking. – Andrew Spott Apr 26 '12 at 17:10
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Do you plug in, wake from sleep, go back to sleep and unplug often? You might need to reset your SMC. I've been having similar issues, but with little to know load and I think it's due to my SMC. I wonder if this discussion will help you: High fan speed and CPU temp with low CPU usage?

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