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Something on my new MacBook Air 2011 is eating up the CPU and battery, with 30% User CPU in Activity Monitor, but there is no process listed with high CPU usage. Temperature is also very high. What could be happening?

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up vote 1 down vote accepted

Activity Monitor and sampling tools like top do cull processes that have terminated, so it's possible something is spawning lots of short lived processes.

Also, try changing the sample time to see if it's a rounding error. I have seen activity monitor lag RAM changes by 15 to 60 seconds so there could be measurement errors - especially with hyper threading on the new i5/i7 chipsets.

If you really want to dig into this, you might need to fire up Instruments from Xcode. Also, command tools like top, vm_stat, io_stat, and fs_usage.

The dtrace tools are powerful, but might be worse if you don't have long running processes or want to learn the syntax.

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Yes -- I discovered this was actually LyX's "Instant Preview" feature gone awry, apparently starting up many dvipng processes that were quickly exiting. That's why they were showing up as 0% CPU. Thanks much! I couldn't try the Instruments tip, but will keep this in mind if it happens again. – PBJ Oct 7 '11 at 3:26

In Activity Monitor, switch to the "All Processes" instead of "My Processes" and see if there are any high-CPU-usage apps there.

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In Activity monitor, there should be a drop-down menu that in your case probably says "My Processes." Click on that, and select "All Processes." This will show all of the running processes (sometimes, processes that you don't own are grouped under "User"). Alternatively, if the disk activity is high, you might want to try running iosnoop to figure out what your disk is doing that might cause such high disk activity.

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It's already on All Processes. – PBJ Oct 7 '11 at 0:43

Try running in Terminal fs_usage (as root) which would show you system calls and page faults related to filesystem activity in real-time. You will see which process it is.

Eventually you may run: top -o cpu (as root).

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