Windows 10 Guest wastes (constantly uses) a full CPU core on the Host, non-stop, even when Guest is not using CPU

[Jacob Klein]

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Problem:

Windows 10 Guest wastes (constantly uses) a full CPU core on the Host, non-stop, even when Guest is not using CPU.
Windows 8.1 Guest does not waste a full CPU core on the Host.

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VMs: ​https://developer.microsoft.com/en-us/microsoft-edge/tools/vms/

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Problem Behavior:

Guest: MSEdge.Win10.VirtualBox - v1809 - Build 17763.379 - October 2018 Update (VM Build 20190311)
-> Guest used CPU non-stop for ~30 mins (mscorsvw, ngen, wsappx, Windows Update, Antimalware Service Executable)
-> Host showed VirtualBox.exe/VirtualBoxVM.exe using a full core non-stop
-> Even after ~30 mins, when Guest stopped using CPU, host STILL showed a full core being used by VirtualBox.exe/VirtualBoxVM.exe
-> Guest - Went to Windows Update and clicked Restart, which updated to: v1809 Build 17763.379
-> Host STILL showed a full core being used by VirtualBox.exe/VirtualBoxVM.exe
-> Repeated for another Windows Update, updating to v1809 Build 17763.914
-> Host STILL showed a full core being used by VirtualBox.exe/VirtualBoxVM.exe
-> Tried Shutdown then Start -> Normal Start
-> Host STILL showed a full core being used by VirtualBox.exe/VirtualBoxVM.exe

For all tests:
Paravirtualization Interface: Hyper-V

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Host: Windows 10 Insider Fast v2004 Build 19041.1, Oracle VirtualBox v5.2.35 Test Build 135314

Guest: MSEdge.Win10.VirtualBox - v1809 - Build 17763.379 - October 2018 Update (VM Build 20190311)
-> VirtualBox.exe using a full core non-stop!

Guest: IE11.Win81.VirtualBox (VM Build 20180102)
-> VirtualBox.exe does NOT use a full core! (Guest uses some CPU, but when Guest stops using it, host stops using it)

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Host: Windows 10 Insider Fast v2004 Build 19041.1, Oracle VirtualBox v6.0.15 Test Build 135299

Guest: MSEdge.Win10.VirtualBox - v1809 - Build 17763.379 - October 2018 Update (VM Build 20190311)
-> VirtualBoxVM.exe using a full core non-stop!

Guest: IE11.Win81.VirtualBox (VM Build 20180102)
-> VirtualBoxVM.exe does NOT use a full core! (Guest uses some CPU, but when Guest stops using it, host stops using it)

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Host: Windows 10 Insider Fast v2004 Build 19041.1, Oracle VirtualBox v6.1.0 Build 135406

Guest: MSEdge.Win10.VirtualBox - v1809 - Build 17763.379 - October 2018 Update (VM Build 20190311)
-> VirtualBoxVM.exe using a full core non-stop!

Guest: IE11.Win81.VirtualBox (VM Build 20180102)
-> VirtualBoxVM.exe does NOT use a full core! (Guest uses some CPU, but when Guest stops using it, host stops using it)

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Host: Windows 10 Release v1909 Build 18363.535, Oracle VirtualBox v5.2.35 Test Build 135314

Guest: MSEdge.Win10.VirtualBox - v1809 - Build 17763.379 - October 2018 Update (VM Build 20190311)
-> VirtualBox.exe using a full core non-stop!

Guest: IE11.Win81.VirtualBox (VM Build 20180102)
-> VirtualBox.exe does NOT use a full core! (Guest uses some CPU, but when Guest stops using it, host stops using it)

==============================================
Host: Windows 10 Release v1909 Build 18363.535, Oracle VirtualBox v6.0.15 Test Build 135299

Guest: MSEdge.Win10.VirtualBox - v1809 - Build 17763.379 - October 2018 Update (VM Build 20190311)
-> VirtualBoxVM.exe using a full core non-stop!

Guest: IE11.Win81.VirtualBox (VM Build 20180102)
-> VirtualBoxVM.exe does NOT use a full core! (Guest uses some CPU, but when Guest stops using it, host stops using it)

==============================================
Host: Windows 10 Release v1909 Build 18363.535, Oracle VirtualBox v6.1.0 Build 135406

Guest: MSEdge.Win10.VirtualBox - v1809 - Build 17763.379 - October 2018 Update (VM Build 20190311)
-> VirtualBoxVM.exe using a full core non-stop!

Guest: IE11.Win81.VirtualBox (VM Build 20180102)
-> VirtualBoxVM.exe does NOT use a full core! (Guest uses some CPU, but when Guest stops using it, host stops using it)

[rseiler]

Yup, issue. Workarounds in the meantime?

[rseiler]

Continues with 6.1.2 Build 135663. This isn't surprising for an unacknowledged bug, but I thought it worth pointing out before someone asks.

The floor is still one core.

[rseiler]

Just wanted to add this: ​https://i.imgur.com/UKyZamN.png

It depicts the CPU use on the host (showing the 25%, 1 core, in my case), the flat Task Manager of the guest, and the Session Information window showing very little.

[aeichner]

Please attach a VBox.log of the affected VM so we can at least try to reproduce the issue with a config close to yours.

[rseiler]

I'm sure the OP will get to that at the first opportunity, but are you saying that it hasn't reproduced for you so far? The OP and I likely have randomly different hardware, and so far, neither of us has managed not to reproduce it (with a Win10 VM on a Win10 host).

[Jacob Klein]

I have attached the requested log files, generated from:

• Oracle VirtualBox v6.1.2 Build 135663
• Host: Windows 10 Release v1909 Build 18363.628
• Guest: Windows 10 Release v1809 Build 17763.379

The problem happens using any Windows 10 Guest. But if you need an immediate example, you can still get a Windows 10 Guest at this URL:
​https://developer.microsoft.com/en-us/microsoft-edge/tools/vms/

The problem persists - A full CPU core is wasted on the host. My host has 8 cores, 16 threads, so I continuously see 6.25% CPU wasted, confirmed via both Task Manager's Details tab and Process Explorer.

Are you able to reproduce the issue?
Can you please acknowledge that you can reproduce the issue?
And can you please fix it?

Note: It looks like Microsoft has removed the older OS VMs from that URL, but I still have them locally, and can provide them upon demand. I assure you that Windows 8.1 Guest does not waste the host's CPU, but Windows 10 Guest DOES waste the host's CPU. As per the original post.

Looking forward to a helpful reply,
Jacob Klein

[rseiler]

Continues with 6.1.4. This isn't surprising for an unacknowledged bug, but I thought it worth pointing out before someone asks.

[aeichner]

I tried to reproduce it with the Windows 10 VM provided by MS. At first I was able to see the issue though it took quite some time for the guest to settle down because it installed a huge amount of updates. However after shutting down the VM and starting again which installed the updates it vanished and didn't appear again so far. Maybe some of the Windows updates fixed it, did you install all the available updates inside the guest? What we noticed is that the guest programs the periodic RTC timer of the VM to 2048Hz which is quite a lot but seems to be common among Windows 10 and we didn't observe this with other Windows 10 guests so far.

[rseiler]

Yes, I've verified this with a fully updated VM and even a freshly-installed and updated one with 1903/1909 (i.e. later than the pre-built one provided by MS). So, whatever solved it on your end, I don't think it was that. Perhaps it comes down to something about differences in host hardware.

Re "periodic RTC timer of the VM to 2048Hz," which I'd have to research to perhaps understand, let me know if there's something in that area to test.

[aeichner]

One of my co-workers found out that adding another vCPU or switching to the ICH9 chipset (which enables the HPET) helps as well. He also could still reproduce the issue after a full update.

[rseiler]

I'm happy to confirm that switching to ICH9 does work.

[Jacob Klein]

I will try to test this soon, but is there any way to make it "not waste CPU" by default somehow?

[aeichner]

We need to investigate where this issue comes from as not all Windows 10 guests seem to be affected but it might take some time.