I have the problem described in the question. There was the same question on quora a year back, however, none of the proposed answers - which were more about what might be going wrong than how to repair the situation - did go in any direction that would help me.
My system:
- Ubuntu 18.04.1 LTS, 64 bit
- 64 GB of RAM
- intel core i7 6700K CPU 4 GHz x 8
I have given 32 GB of RAM and 4 Processors to the virtual machine.
When the ubuntu box is started, the windows guest runs smoothly and fast. Over time of the uptime of the ubuntu host, the guest system slows down - in my opinion, this slowing down process is linked to the uptime of the host, not the runtime of the guest.
I checked that:
- RAM consumption on Host and Guest are low (i.e., plenty of ram left on the host and the guest nearly not consuming anything)
- CPU consumption low on Host and Guest
I am working with snapshots that I perform regularly. Making snapshots does not speed up the guest.
I am often completely shutting down the guest and restarting (both using ACPI shutdown and reset). Not speeding up the guest.
I am completely unable to pinpoint why the guest would be slow.
I can provide the VM logs as I am unable to use them myself (I have no idea what I might be looking for).
Any help would be appreciated - note that the obvious "workaround-solution", restarting the host, is not an option as I have long-running processes on that machine that I do not want to interrupt.