Windows guest on linux host is very slow with guest additions

[albion]

I have installed VBox on an Archlinux x64 host (Manjaro). The guest is Win 8.1 Update 1 x64. I use a Core2Duo 9500M having hardware virtualisation enabled. With guest additions installed the guest becomes very slow oftentimes even unresponsive (often taking several seconds to draw a Window.) In the guest's task manager the CPU load is already 20-50% usage when system is shold be idle. It shows the system interrups process with 10-20% usage. And just having Skype running without conversation for example, causes overall CPU usage of nearly 100%.

Without installing the guest additions the guest seems to be much faster and system interrups cause < 3% usage.

[frank]

Could you check the guest task manager for processes hogging the (guest) CPU? Could you also attach a VBox.log file of such a VM session?

[albion]

The VBox version is 4.3.10 instead of 4.3.12

[frank]

Any improvement with VBox 4.3.20?