How do I enable multiple cores in my virtual enviroment?

Question

I've installed Ubuntu in a virtual environment using Oracle VM VirtualBox Manager and it works great.

However I'd like to enable multiple cores - as seen in the image below my Windows machine has 2 cores:

Now when I run the lscpu in Ubuntu I get the following info revealing that only 1 core is being utilized:

I've tried changing the settings of the virtual box to enable multiple processors but it won't allow me to do so as shown in the image below:

How do I enable multiple cores (processors) in my virtual enviroment?

Answer 1

To enable more than 1 CPU in your VM the following settings are needed in addition:

• 64-bit virtual guest hardware in General settings tab (for 64-bit guests)

  

• enable I/O APIC in the Motherboard settings tab

  

• enable hardware virtualization (VT-x/AMD-V) in the Acceleration tab

  

Note that if your run your VM on all cores available you may experience a better host performance when assigning an execution cap to the CPU.

If you had not enabled hot-plug CPU feature of virtualbox changing of the number of cores can only be done on a machine that was shut down.

A performance boost in the guest is only to be expected for software that makes use of several cores. Only then giving all cores with an execution cap makes sense.

Answer 2

If your VM is currently running (or "Saved") you can't change that value. Power off your VM first.

Answer 3

I was working on a multithreaded program which executed in sequential order on virtual machine. I had similar problem as you had. I fixed it by :

1. Stop virtual machine or exit.
2. Launch VMWare --> Select machine -->Click System --> Click Processor --> Change number processors.
3. Start Virtual Machine.

Earlier std::thread::hardware_concurrency() from standard thread returned 1, but, after changes it returns the number of CPU's on the settings of Virtual Machine.

Now, I was able to run my multithreaded programs on VM successfully.

Answer 4

The other answers didn't work for me, so I'm sharing my solution which is based on VirtualBox manual §2.4 CPU Hot-Plugging.

The GUI allowed me to add 32 vCPUs, but when the Linux guest booted nproc and cat /proc/cpuinfo would only show a single CPU/core/thread. I could see in dmesg that 32 vCPUs were detected:

# dmesg | grep -E 'smp:|smpboot:'
[    0.000000] smpboot: Allowing 32 CPUs, 31 hotplug CPUs
[    0.192151] smpboot: CPU0: Intel(R) Xeon(R) Gold 6148 CPU @ 2.40GHz (family: 0x6, model: 0x55, stepping: 0x4)
[    0.193848] smp: Bringing up secondary CPUs ...
[    0.193850] smp: Brought up 1 node, 1 CPU
[    0.193852] smpboot: Max logical packages: 32
[    0.193854] smpboot: Total of 1 processors activated (4788.97 BogoMIPS)

Seems hotplug is enabled, but the CPUs are not online for some reason.

Run the following on the host:

for i in {1..31}; do VBoxManage controlvm $VM plugcpu $i; done

From within the guest I can see the CPUs have been hotplugged, but they are not automatically put online:

# dmesg | grep 'has been hot-added'
[  317.236099] CPU1 has been hot-added
[  317.289383] CPU2 has been hot-added
[  317.341704] CPU3 has been hot-added
[  317.393434] CPU4 has been hot-added
[  317.602969] CPU5 has been hot-added
[  317.603570] CPU6 has been hot-added
[  317.603810] CPU7 has been hot-added
[  317.604031] CPU8 has been hot-added
[  317.780191] CPU9 has been hot-added
[  317.780498] CPU10 has been hot-added
[  317.780745] CPU11 has been hot-added
[  317.817875] CPU12 has been hot-added
[  317.870629] CPU13 has been hot-added
[  317.911276] CPU14 has been hot-added
[  317.962533] CPU15 has been hot-added
[  318.012838] CPU16 has been hot-added
[  318.063693] CPU17 has been hot-added
[  318.116346] CPU18 has been hot-added
[  318.167847] CPU19 has been hot-added
[  318.232230] CPU20 has been hot-added
[  318.284266] CPU21 has been hot-added
[  318.344941] CPU22 has been hot-added
[  318.373422] CPU23 has been hot-added
[  318.501419] CPU24 has been hot-added
[  318.501714] CPU25 has been hot-added
[  318.535717] CPU26 has been hot-added
[  318.652636] CPU27 has been hot-added
[  318.653046] CPU28 has been hot-added
[  318.689386] CPU29 has been hot-added
[  318.739736] CPU30 has been hot-added
[  318.790743] CPU31 has been hot-added

# nproc
6

But you can bring the CPUs online manually from within the guest by running:

# for CPU in /sys/devices/system/cpu/cpu*/online; do echo 1 | sudo tee $CPU >/dev/null; done

Healthy:

# nproc
32

This appear to persist when the guest is rebooted:

# dmesg | grep -E 'smp:|smpboot:'
[    0.000000] smpboot: Allowing 32 CPUs, 0 hotplug CPUs
[    0.189487] smpboot: CPU0: Intel(R) Xeon(R) Gold 6148 CPU @ 2.40GHz (family: 0x6, model: 0x55, stepping: 0x4)
[    0.191502] smp: Bringing up secondary CPUs ...
[    0.278723] smp: Brought up 1 node, 32 CPUs
[    0.278723] smpboot: Max logical packages: 1
[    0.278723] smpboot: Total of 32 processors activated (153236.67 BogoMIPS)