I'm trying to debug why 20% of 3 CPUs is being used in the host, while the guest CPU is idle. This is for a Windows 10 guest.

 

I ran across this page that seems to indicate that we can use either viostor or vioscsi drivers. I blindly installed both. Elsewhere I saw that viostor performed better, but had fewer features. I'd like to try switching virtio driver to see what that does to my host CPU usage.

 

Does this make sense, or am I on a wild goose chase?

 

Next question: How do I persuade Windows to install the other drivers? I'm afraid that if I uninstall the existing drivers I won't be able to boot the OS.

You can't use two drivers for one device, only one can be used by a device at the same time. If you want to change the driver you just have to update the controller driver in the device manager. I use the viostor driver.

Yeah. I'm not suggesting I'd use two drivers.

 

How do I update the driver in device manager? Windows just keeps telling me that I'm already using the best driver for my device.

If I select "Red Hat VirtIO SCSI Disk Device" and try to install the viostor driver, I get "The folder you specified doesn't contain a compatible software driver for your device."

Which folder did you exactly select?

 

You have to select viostor/(your windows version)/(x86 or x64, you are probably using x64)

Yeah. I'm not suggesting I'd use two drivers.

 

How do I update the driver in device manager? Windows just keeps telling me that I'm already using the best driver for my device.

Here is how I forced Windows 10 to use an older driver for my Laptop's NIC.  NOTE you may have to take steps to turn off auto upgrade too - I already did that.

 

• Find device in device manager and choose upgrade driver.
  
• "Browse my computer for driver software"
  
• "Let me pick from a list of device drivers on my computer"
  
• "Have Disk..."
  
• "Browse" - to the software .inf file for my nic
  
• Select appropriately listed driver from window then click "next"
  
• Let it install the driver.
  
• Hope windows doesn't upgrade the driver automatically if you still have auto upgrades turned on or go here first http://winsupersite.com/windows-10/stop-automatic-driver-updates-windows-10 Although there is some doubt what they say works I turned off ALL upgrades like a poster suggested
  

Hope that helps

I'm trying to debug why 20% of 3 CPUs is being used in the host, while the guest CPU is idle. This is for a Windows 10 guest.

 

I ran across this page that seems to indicate that we can use either viostor or vioscsi drivers. I blindly installed both. Elsewhere I saw that viostor performed better, but had fewer features. I'd like to try switching virtio driver to see what that does to my host CPU usage.

 

Does this make sense, or am I on a wild goose chase?

 

Next question: How do I persuade Windows to install the other drivers? I'm afraid that if I uninstall the existing drivers I won't be able to boot the OS.

 

I don't think that the driver used for the vdisk has anything to do with your host CPU being 20%.

 

The host is using a primary vDisk Bus of virtIO despite the driver used in the guest. If you have a driver using a lot of CPU then it would reflect on the guest CPU usage as well. It couldn't use the host CPU without making an impact on the guest CPU. To me, that doesn't make sense but maybe I am missing something here?

 

Anyway if changing drivers etc and you are worried about the VM not starting. Just backup the vdisk before you start, so you can roll it back if needed.

 

edit.........  You could check how much cpu is being used for the emulation parts of the VM by splitting them/isolating them off. Using emulatorpin.

 

A quad core intel would be paired like this

0  4 .  core1

1  5 .  core2

2  6 .  core3

3  7 .  core4

 

now as unraid likes to use core 1 for its functions leave that alone.

Look at the xml below

 

 <cputune>
    <vcpupin vcpu='0' cpuset='2'/>
    <vcpupin vcpu='1' cpuset='6'/>
    <emulatorpin cpuset='3,7'/>
  </cputune>

 

This would pin core 3 to the windows vm

Then it will pin the emualtor functions to core 4

 

So now you could stop all dockers and other vms etc. Fire up the windows 10 vm and you will be able to see which cores are being used.

If core 4 (3,7) is high then the 20% you are seeing in the host should reflect here as its the emulation function overhead of running the vm. if you see it in the core 3 then it is in the vm itself and for some reason you are not seeing it in task manager.

 

Now you could take this a step further even by isolating those 2 cores in your syslinux config file so unRAID cant even use those 2 cores at all. but its not really necessary for testing this.