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just purchased a 2010 Mac Pro, running High Sierra. It has 12 lovely cores.

But, when I look at the CPU activity in the CPU History half of the rows are blank (image below).

Does this suggest one of my CPUs isn't working?

  • Does this happen even when you're doing CPU heavy based tasks? – Andre Feb 15 '18 at 10:40
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Each alternate line is a hyper threaded core, not a real core - count the lines, there are 24, not 12.

If you're doing something processor-intensive, it makes more sense to use real cores, so tasks first share out to all the top line of each virtual pair.

Edit for new image
Image showing

  • to the left - 2 simultaneous [yet separate apps] 3rd party app video conversions, still only the real cores needed - presumably the app threads according to the number of actual cores, for speed. If you add more tasks, they will start to add to the 2nd virtual core, but HT isn't as fast as 'real' for intensive tasks.
  • to the right - a single conversion from Final Cut Pro, showing much better 'spread' of resources.

I'm sure someone will come along with a better technical explanation, but in short - no, it's not broken, both CPUs are functioning normally, but maybe the software isn't fully using all the resources.

I have no explanation for why FCP would work differently to 'regular' conversion apps, but the picture shows the difference.

  • Apple documents this on their site: support.apple.com/en-us/HT202060 – Allan Feb 15 '18 at 11:13
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    Well, same as the other answer... but that page does not explain the precedence of the 'leading' core at all. The aggregate it refers to is shown in the main Activity Monitor window; not the cores window. Though that page looks like it was last actually updated when the 3,1 was new :/ – Tetsujin Feb 15 '18 at 12:03
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    Revised the answer using FCP which does show usage in all cores. – Tetsujin Feb 15 '18 at 12:24
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No, this is not an indication of anything being wrong with your CPU.

You have a 2 x 6 core CPUs = 12 cores. There are 24 rows in your CPU history, and there's activty in 12 of them. I.e. every core is accounted for.

The reason that you have extra rows are probably that your CPU supports HyperThreading. HyperThreading does not mean that you have double the amount of cores, but rather that in some (rarer) cases, the system might be able to run two operations at the same time on a single core.

So everything is as it is supposed to be.

  • @Tetsujin I have edited the answer to remove the reference to the old KB. No need to post the same answer twice. – jksoegaard Feb 15 '18 at 12:18

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