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Suddenly this morning my macbook pro became extremely slow and laggy. Just performing trivial tasks such as right-clicking, marking an icon, opening activity monitor, scrolling a web page, changing the active window, orchanging safari tabs will leave the mac in a frozen state for 20-40 seconds. I'm typing this post half-blind, as what I type only shows some 10 seconds later.

Some specs:

  • macOS Sierra 10.12.1

  • MacBook Pro, 13", Mid 2012

  • 2.9 GHz Intel Core i7

  • 8GB RAM 1600 MHz DDR3

In Activity Monitor, strangely, most active processes are listed with a 0.0% CPU usage. Why would that be?

I have also reset the SCM and PRAM, with no apparent improvements. The hardware diagnostics said nothing was wrong. Disk Utility repair said everything seems to be okay with the volume. Attached are some screen shots of activity monitor. I could post some console output as well, but I don't know what is relevant.

I really have no idea of what is going on. The computer has never lagged like this. Recently, about a month ago, a certified Apple repair shop replaced the logic board, but that should not affect this, right? I am currently backup up my data, preparing for a clean install of the OS, but copying files is taking a very long time. I will report back when that is done. Does anyone have any idea of why this might happen?

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  • A clean install of macOS may be the way to go (as you intend to do), but I'm just wondering whether you've tried starting it is Safe Mode to see if the behaviour continues? To do this, hold down the SHIFT key during startup. It will take a little longer to start, but once it's finished you'll be able to test whether the lag continues.
    – Monomeeth ♦
    Dec 6, 2016 at 1:44
  • Yes, same lag in safe boot. What does this mean?
    – Yoda
    Dec 6, 2016 at 7:34
  • At the risk of oversimplifying things, it basically means it's not a 3rd party software issue. In other words it has to be either a hardware issue or a corrupted macOS installation. Doing a clean install of macOS is now a good way to go as your next step.
    – Monomeeth ♦
    Dec 6, 2016 at 7:57
  • When I try to erase the disk using Disk Utility frim Internet Recovery, I get an error. "Unmounting disk... Couldn't unmount disk... Operation failed."
    – Yoda
    Dec 6, 2016 at 8:36
  • I'm thinking it could be a hard drive issue. Either the hard drive speeds are low or it needs to be repaired by software or it could be dying. Try opening disk utility and repairing the disk and disk permissions. (This suggestion is only valid on non-retina MBPs - with spinning HDDs.)
    – NoahL
    Dec 6, 2016 at 15:59

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I have no reputation to comment, so I will give my answer:

  • While it's hard to believe, the logic board thing in the Apple Store may have something to do with your lag. If I was you, I'd definitively go on the Apple Store that made the process and ask for some re-check. However, as you said it's been some time, the problem should not appear now, but when you first turned it on. I'd still go on the Apple Store.
  • Do you have secondary disks, like a Bootcamp one for Windows? I'd check them, maybe repair them.
  • Run MalwareBytes for macOS: https://malwarebytes.com/mac-download/
  • Erasing your Mac to the originals seems like the best option if the answer is not viruses or disk bugs. I'd go for this one after going to the Apple Store
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