I have a late 2013 6-cpu Mac Pro running Big Sur. Within the past month or so, I'm getting cpu spikes lasting 5-10 minutes. Activity monitor shows kernel task consuming >800% CPU. I ran spindump and discovered that of 17 seconds (!) of time in kernel task, there were 10 or so threads consuming about 14sec of cpu, with

*319 slave_block + 37 (AppleIntelCPUPowerManagement + 22430) [0xffffff80017ab79e]

in the call stack. All the threads were blocked waiting on machine_switch_context, a couple were in some forced idle call and one looks like it was in some queue wait.

So what's changed over the past couple months? A couple of Big Sur updates, and the addition of MS office software; I really needed ms remote desktop functionality. Also updates from Avid, their bg processes use a lot of resources.

Any ideas or suggestions? It wouldn't break my heart to remove MS if I can find a suitable RDC replacement.

BTW, has anyone noticed the swastika-like nature of the MSRDC icon? Just sayin'

  • MS RDC is not part of office. You can get it separately, freeware, App Store.
    – Tetsujin
    Commented Jan 12, 2023 at 7:30
  • I think I just fixed a similar issue by cleaning the stripe-like holes at the bottom of the case for my macpro 2013. The fan is supposed to pull air from those holes which were all blocked with dust lol.
    – yijiem
    Commented Mar 12, 2023 at 20:21

1 Answer 1


You should consider that the change might not be due to software you have installed over the course of a few months - but instead from hardware issues.

If the system cannot provide sufficient cooling for the CPU, the power management software inside the kernel will try to idle the CPU in order to bring down the CPU temperature. This could be triggered by for example a build up of dust in the system fan, the system fan failing or near failing, and similar.

The "trash can" Mac Pro has a single, big fan that cools the entire system. I would give it a check to ensure that everything is working properly.

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