The future of Virtualbox on Windows is grim

[bobofet]

Summary of the issue

On my Thinkpad with Windows 11 Pro, Virtualbox's performance is atrocious with a high number of processors, due to extreme slowdown and CPU stalling the more CPUs you assign to the guest. Guests can sometimes fail to boot due to a soft CPU lockup, and if they do boot, it takes over 5 minutes.

Reducing the CPU count quadruples the performance and stops boot failures.

At Klaus's request I did exhaustive comparison tests based on number of CPUs.

Hardware and OS:

• Brand new Lenovo Thinkpad P16s Gen2. CPU is AMD Ryzen 7 Pro 7840U (8 cores, 16 threads), 64GB RAM, Windows 11 Pro 64-bit, Virtualbox 7.18, running on a SSD. Everything in Windows was at default the way it was shipped to me from Lenovo (except for some privacy/advertising settings in Windows).
• Confirmed virtualization is allowed in BIOS
• The Powershell command "Get-WindowsOptionalFeature -FeatureName Microsoft-Hyper-V-All -Online" returns "State: Disabled".
• The graphical "Turn Windows features on or off" menu shows everything under Hyper-V is unchecked.
• msinfo32 shows 'Virtualization-based security: Running". Further details in attached screenshot.

Test details

• I created a basic VM with 8192MB RAM using the VBox New Machine wizard. Everything is at default, except: I inserted Ubuntu 24.04 Desktop ISO in optical drive, and I unplugged the network adapter cable. The only variable between tests is CPU count.
• I am testing "time to desktop". I boot the empty VM, which is booting from USB since there's no OS, I select "Try or install Ubuntu" and start the stopwatch, I wait for the desktop to load and Ubuntu shows a language selection dialog, then I stop the stopwatch. Then I Reset the VM, and do another run.
• I remind you I have a laptop, and Windows/Lenovo power savings algorithms (even though I am plugged into power) can affect CPU performance. I only had Firefox open while doing these tests.
• When I say "soft CPU lockup" it's the "watchdog - BUG - soft lockup - CPU #0 stuck for 21s [swapper/0:1]" message in the guest. Sometimes it shows another CPU number.
• In all tests, "Snail Mode" was active (green turtle icon in Vbox systray)

Test results (How long it takes to get to Ubuntu desktop)

1 CPU:

• 2m
• 2m24s
• 2m10
• 2m20
• 2m30
• FAILED: unique issue likely unrelated to Vbox : it got to the desktop but remained a black screen (cursor changed, but no desktop background or any windows visible, heard the Ubuntu jingle at 2m40s). I gave up at 5m.
• 1m50s

2 CPU:

• 1m55s
• 1m40s
• 1m40s
• 1m40s

3 CPU:

• 1m48s
• 1m48s
• 1m33s
• 1m40s
• 1m40s

4 CPU:

• 1m40s
• 1m48s
• 1m38s
• 1m40s

5 CPU:

• 3m
• 2m
• 2m30s
• 2m20s
• 2m40s

6 CPU:

• 4m10s
• 6m
• 3m20s
• 9m
• FAILED: soft CPU lockup
• FAILED: soft CPU lockup
• FAILED: soft CPU lockup (after this I did a Power Off instead of Reset)
• 3m37s
• 6m
• 4m40s

7 CPU:

• 7m
• FAILED: soft CPU lockup
• 4m10s
• FAILED: soft CPU lockup
• FAILED: soft CPU lockup

8 CPU:

• FAILED: soft CPU lockup
• FAILED: soft CPU lockup
• 6m30s
• FAILED: soft CPU lockup
• 6m

[bobofet]

guest prints this in both good and bad boots

[bobofet]

Logs for the 3 runs in comment #1

[bobofet]

Moved.

[bobofet]

Moved.