Limiting a KVM (Windows) or Virtual Machine CPU resources

[Giovanni]

Hello guys

I was able to setup Windows Server 2003 without a hitch on my Q6600 Core2.

I am able to assign it RAM / Disk space so I know it won't go over that.

Now, I installed Prime95 an utility used by Overclockers to do iterations and max out memory/cpu to proof test the ability to handle the load of the VM.

When I created the VM, the settings where:

CPUs = 1
CPU Units = 1000

Fine, so I load Prime95 and keep the VM at full load and the server load goes to 100% use (when you hit "Home" to see the server as a whole).

I lower the number CPU units to 100, no change, 50 now we get 25% top usage on the server as a whole.

I changed 50 to 25 now and I can't get the server (as a whole) load to go below 25% CPU load while the VM is at 100% CPU... help please

 

[tom]

you got 4 cpus on the host.

and 1 cpu on the guest: this is 25 % of the host cpu.

 

[Giovanni]

you got 4 cpus on the host.

and 1 cpu on the guest: this is 25 % of the host cpu.

Understood, however I want to limit that single CPU I gave the Guest OS.

Possible? I thought thats what CPU units where for. What are CPU Units?

 

[Nemesiz]

Understood, however I want to limit that single CPU I gave the Guest OS.

Possible? I thought thats what CPU units where for. What are CPU Units?

As i know CPU units its for reserve 'minimum' CPU resources for VM. VM can use all CPU resources, but it can by limited when another VM is actyve too.

 

[Giovanni]

As i know CPU units its for reserve 'minimum' CPU resources for VM. VM can use all CPU resources, but it can by limited when another VM is actyve too.

Thanks.

I am trying this theory out, but so far my CPU load is 100% (for this Quad core).

Keep in mind all settings are CPUS = 1 on all 4 VMs. See attached

 

[Giovanni]

Interesting, all 4 VMs are doing the same thing and it seems like KVM pairs them up to "share" memory? (I still have a little of SWAP usage)

 

[tom]

Interesting, all 4 VMs are doing the same thing and it seems like KVM pairs them up to "share" memory? (I still have a little of SWAP usage)

the memory shown for windows guest is not really perfect. for Linux guest its better but also not perfect. maybe you should jump into the KVM mailing list, there is a discussion about improving this (KSM).

 

[Giovanni]

Is it possible to limit how many Mhz we give to a VM/KVM? I believe its possible since HyperVM seems to do it they use OpenVZ

 

[dietmar]

I was possible with older openvz kernels (<= 2.6.18). But the OpenVZ team did not implement this with newer kernels.

 

[Giovanni]

I was possible with older openvz kernels (<= 2.6.18). But the OpenVZ team did not implement this with newer kernels.

Hmm, I will research this further. Can you please point me in the direction where proxmox VE saves the "init" values for KVM/OpenVZ virtual machines?

Let's say I saw a line to start the VE in the OpenVZ forums and it seems to work, is there any way to hard-code it into Proxmox so every time I start (just that one VE) it will use say "cpulimit=512"?

Same goes for KVM I know its a different environment so it may have two answers for the two case scenarios.

Thanks

 

[dietmar]

OpenVZ config:

directory: /etc/vz/conf/
docu: "man vzctl"

KVM config:

directory: /etc/qemu-server
docu: "man qm"