virtualbox.org

I've only recently discovered VirtualBox and I already can't live without it. I'm using Windows 8.1 as the host and a Fedora 20 KDE guest running in seamless mode. All of it runs swimmingly with guest additions.

Host has an i7 with 8 logical cores, 8 GB of RAM. Guest has 4 of those cores, 4 GB of RAM (info at bottom).

Then, I discovered CPU hotplugging. What a cool feature! Except that I can't get it to work while the VM is on (with vboxmanage controlvm name unplugcpu x) no matter what I try. I have followed the directions listed in chapter 9.5 of the manual in order to enable hotplugging (I can't post the link for what I assume are anti-spam reasons).

Plugging and unplugging works just fine on the command line with the VM powered down, but when it's powered up any attempt to unplug a CPU results in the following error:

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VBoxManage.exe: error: Hot-Remove was aborted because the CPU may still be used
by the guest
VBoxManage.exe: error: Details: code VBOX_E_VM_ERROR (0x80bb0003), component Con
sole, interface IConsole, callee IUnknown
VBoxManage.exe: error: Context: "HotUnplugCPU(n)" at line 135 of file VBoxManage
ControlVM.cpp

Now, if I understand correctly, the guest additions should automatically be capturing the hotplug event and shutting the processor down so that it can be unplugged, right? That doesn't seem to be happening here for me.

Since there's something about that exact error message for Linux guests listed in the manual, my next step was to manually shut off the processor, which is what I assume the GA process is supposed to do automatically:

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echo 0 > /sys/devices/system/cpu/cpuX/online

After ensuring that the processor was off (it stopped showing up in htop), I went back to trying to unplug the CPU with the VM running and the processor for sure not being used by the guest, only to get the same error.

Next, I spent a couple hours trolling these forums and Google trying to find someone who has the same problem, and have come up empty, so I have finally registered an account to ask this question. What am I doing wrong? Is that error an actual bug?

Output of vboxmanage showvminfo:

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Name:            FedoraDesktop
Groups:          /
Guest OS:        Fedora (64 bit)
UUID:            5fffe2c1-720a-4f82-beba-a37954f4bf9c
Config file:     D:\FedoraDesktop\FedoraDesktop.vbox
Snapshot folder: D:\FedoraDesktop\Snapshots
Log folder:      D:\FedoraDesktop\Logs
Hardware UUID:   5fffe2c1-720a-4f82-beba-a37954f4bf9c
Memory size:     4096MB
Page Fusion:     off
VRAM size:       128MB
CPU exec cap:    100%
HPET:            off
Chipset:         piix3
Firmware:        BIOS
Number of CPUs:  4
PAE:             on
Long Mode:       on
Synthetic CPU:   off
CPUID overrides: None
Boot menu mode:  message and menu
Boot Device (1): Floppy
Boot Device (2): DVD
Boot Device (3): HardDisk
Boot Device (4): Not Assigned
ACPI:            on
IOAPIC:          on
Time offset:     0ms
RTC:             UTC
Hardw. virt.ext: on
Nested Paging:   on
Large Pages:     on
VT-x VPID:       on
VT-x unr. exec.: on
State:           running (since 2014-02-19T16:16:35.246000000)
Monitor count:   1
3D Acceleration: on
2D Video Acceleration: off
Teleporter Enabled: off
Teleporter Port: 0
Teleporter Address: 
Teleporter Password: 
Tracing Enabled: off
Allow Tracing to Access VM: off
Tracing Configuration: 
Autostart Enabled: off
Autostart Delay: 0
Default Frontend: 
Storage Controller Name (0):            IDE
Storage Controller Type (0):            PIIX4
Storage Controller Instance Number (0): 0
Storage Controller Max Port Count (0):  2
Storage Controller Port Count (0):      2
Storage Controller Bootable (0):        on
Storage Controller Name (1):            SATA
Storage Controller Type (1):            IntelAhci
Storage Controller Instance Number (1): 0
Storage Controller Max Port Count (1):  30
Storage Controller Port Count (1):      1
Storage Controller Bootable (1):        on
IDE (1, 0): Empty
SATA (0, 0): D:\FedoraDesktop\FedoraDesktop.vmdk (UUID: 2d4aba11-c659-4ea2-b64e-a172df3aed40)
NIC 1:           MAC: sanitized, Attachment: Bridged Interface 'Qualcomm Atheros AR9485WB-EG Wireless Network Adapter', Cable connected: on, Trace: off (file: none), Type: 82540EM, Reported speed: 0 Mbps, Boot priority: 0, Promisc Policy: deny, Bandwidth group: none
NIC 2:           disabled
NIC 3:           disabled
NIC 4:           disabled
NIC 5:           disabled
NIC 6:           disabled
NIC 7:           disabled
NIC 8:           disabled
Pointing Device: USB Multi-Touch
Keyboard Device: PS/2 Keyboard
UART 1:          disabled
UART 2:          disabled
LPT 1:           disabled
LPT 2:           disabled
Audio:           enabled (Driver: DSOUND, Controller: AC97)
Clipboard Mode:  Bidirectional
Drag'n'drop Mode: Bidirectional
Session type:    GUI/Qt
Video mode:      1920x1046x32 at 0,0
VRDE:            disabled
USB:             enabled
EHCI:            enabled

USB Device Filters:

Index:            0
Active:           yes
Name:             New Filter 1
VendorId:         
ProductId:        
Revision:         
Manufacturer:     
Product:          
Remote:           
Serial Number:    

Available remote USB devices:

<none>

Currently Attached USB Devices:

<none>

Bandwidth groups:  <none>

Shared folders:  

Name: 'win', Host path: 'D:\' (machine mapping), writable

VRDE Connection:    not active
Clients so far:     0

Video capturing:    not active
Capture screens:    0
Capture file:       D:\FedoraDesktop\FedoraDesktop.webm
Capture dimensions: 1024x768
Capture rate:       512 kbps
Capture FPS:        25

Guest:

Configured memory balloon size:      0 MB
OS type:                             Linux26_64
Additions run level:                 2
Additions version:                   4.3.6 r91406


Guest Facilities:

Facility "VirtualBox Base Driver": active/running (last update: 2014/02/19 16:16:50 UTC)
Facility "VirtualBox System Service": active/running (last update: 2014/02/19 16:16:58 UTC)
Facility "Seamless Mode": active/running (last update: 2014/02/19 21:53:57 UTC)
Facility "Graphics Mode": active/running (last update: 2014/02/19 21:53:57 UTC)

I hope I didn't make any glaring etiquette errors. Thanks!

Post the guests *.vbox file ( as a zipped attachment )

As requested.

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<CPU count="4" hotplug="true">
        <HardwareVirtEx enabled="true"/>
        <HardwareVirtExNestedPaging enabled="true"/>
        <HardwareVirtExVPID enabled="true"/>
        <HardwareVirtExUX enabled="true"/>
        <PAE enabled="true"/>
        <LongMode enabled="true"/>
        <HardwareVirtExLargePages enabled="true"/>
        <HardwareVirtForce enabled="false"/>
        <CpuTree>
          <Cpu id="0"/>
          <Cpu id="1"/>
          <Cpu id="2"/>
          <Cpu id="3"/>
        </CpuTree>

OK you have it setup properly. Now to change the CPU count you use modifyvm when off and controlvm when running.

I have tested this on Debian based distros and it works as advertised. Remember you can not unplug 0 as that would kill the system if it were allowed.
so you can plug cpu 1, 2, or 3 and unplug then same. each are independent of the other. You should be able to run cat /proc/cpuinfo and see the change in the guest.

Note 1: monitoring software seems to get torked with this.
Note 2: it tends to be flaky at times. Not sure why.

Post the exact command you are trying to use while running.

Yes, I read that unplugging CPU 0 was not generally allowed, so I've been running all my attempts on CPU 3, then 2 when I couldn't get 3 to unplug.

The exact command I have been using:

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vboxmanage controlvm "FedoraDesktop" unplugcpu 3

As far as I can tell that's the command I should be using to unplug a CPU on a running VM, but when I try it I get the error mentioned above, and the processor stays plugged in and in use on the guest.

I'll fire up my Fedora 20 guest tomorrow and see what happens. What version of VirtualBox are you using?

Version 4.3.6 r91406. I'm using the Fedora 20 KDE spin since Gnome 3 and seamless mode don't seem to like each other. I'm setting up a Debian VM to see if I can get CPU hotplugging to work as advertised there, as you mentioned.

I just want to solve this since I want to move on to hacking up a Java client to poke the API and plug/unplug CPUs automatically for me! I was only trying the command line to make sure I understood how it worked before I started using the API!

Alright. Just remember that VirtualBox deals with actual cores not threads. 8 virtual cores are not the same thing as physical cores. Using all of your cores can cause big issues especially with this feature.

Well, I was able to plug and unplug a CPU at will on a Debian VM--worked exactly as advertised, the processor appeared and disappeared in /proc/cpuinfo right on time. I'm now creating a different Fedora VM just to ensure that it's not something borked with that specific VM, which in retrospect I probably should have tried already.

I've confirmed that I can't plug/unplug a CPU from another Fedora 20 guest while it's running, with the same error. Maybe it's a systemd vs sysvinit problem? Anyone have an Arch guest to test hotplugging on?

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Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Guest

Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Guest

Re: Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Gu

Re: Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Gu

Re: Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Gu

Re: Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Gu

Re: Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Gu

Re: Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Gu

Re: Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Gu

Re: Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Gu

Re: Issues: CPU Hotplugging with Win 8.1 Host & Fedora 20 Gu