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Serious bug: all virtualization software very high CPU usage


macrumors member
Original poster
Mar 1, 2004
Yesterday, I decided to install Yosemite public beta 6 (build 14A388b) and I have stumbled on a serious bug which probably impacts everyone who uses virtual machines(VMs) in any way. A VMWare Fusion (7) VM is nearly unusably slow, while the vmware-vmx process eats up every CPU cycle on every CPU core assigned to the VM. This causes even an idle VM to become unresponsive.

I've converted my VM (running Windows XP with some old software I regularly use) to a Virtualbox VM and, while it works slightly better, exactly the same thing happens: I have one CPU core assigned to the VM and the VirtualBoxVM process constantly uses up all available CPU cycles on that core, constantly running at 100% usage, even when the VM itself is completely idle.

My first thought was a bug in either VMWare Fusion and VirtualBox, but more people on the VMWare support forum also mentioned exactly this problem.

It would appear there's something wrong with Yosemite. Any thoughts?


macrumors member
Aug 27, 2008
exact same experience with Parallels 10. After updating to Yosemite yesterday all of my VMs are so slow they are essentially unusable. Definitely seems to be a bug with Yosemite that is affecting any hypervisor.


macrumors regular
Sep 4, 2001
Indianapolis, IN
Parallels update - performance

Ready for OS X Yosemite!
New Feature: Download Windows 10 Technical Preview from File > New…

This update for Parallels Desktop 10 for Mac build 10.1.0 (28600) addresses overall stability and performance issues, and includes the following fixes:

- Resolves an issue with Parallels Desktop canceling Mac shutdown
- Resolves issues with missing shortcuts to virtual disks on the Mac desktop.
- Resolves a number of issues with visual artifacts in Coherence
- Resolves issues with application window focus in Coherence
- Resolves an issue with Metro apps not launching on Windows
- Resolves an issue with an error splitting a virtual hard disk
- Resolves an issue with Ubuntu 12.04 crashing on restart after Parallels Tools installation
- Resolves an issue with the NumLock key not staying ON
- Resolves an issue with EFI boot enabled virtual machines not starting
- Resolves an issue with the Parallels Tools prl_tg driver failing to install
- Resolves an issue with high CPU usage when connecting a USB device to a virtual machine
- Resolves an issue with the Solid Edge program crashing in a virtual machine


macrumors newbie
Oct 21, 2014
On the VMware side, the issue (which only happens on specific hardware, for example iMac12,2) is being discussed at .


macrumors 65816
Nov 19, 2006
Birmingham, UK
I have not experienced this performance issue you mention on my rMBP. I was running the developer previews since the beginning. I use the latest VMware fusion release.

Have you upgraded to the latest version rather than running the public beta?



macrumors 68030
Apr 23, 2010
I also have no issues with Fusion 7, running Mac, Windows and Linux VM's -no issues on a late 2013 Macbook Retina 15. But I also have 16GB RAM, so I assign 8GB RAM for each VM as I usually only run one at a time, and that helps in performance. Probably overkill though, I suppose 4GB would be enough. . .
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