Why processor use high cpu on KVM?

[Martin Ezequiel]

Hi guys

I need help, I have HP server With Intel Xeon processor 3.10 GHz E1220 v3 and 8 gb ram.

In a kvm has installed windows server 2012 r2 standard. Using RAW format on hard disk.

I have installed many programs, for example mysql.

But the problem in using KVM on idle mode consumes Between 200 and 400 %, Because has assigned 4 cores.

For example in windows (KVM) use about 50 %, but outside in Proxmox consulting in TOP and I see the process KVM uses cpu between 200 and 400 %

I attached captures





Thank you.

 

[swartz]

Where do you see 200 and 400% CPU use?

Your top screenshot says your machine is mostly idle.

 

[longhair]

Could be from the Windows Task Manager - 4 cores at 100% = 400%.

I know my Windows Server 2008 r2 was maxing out the CPU on a clean install.

 

[Martin Ezequiel]

At the time i took the screenshot it wasn't working that hard, but anyway i've been making some more tests, and i'm a little worried about the CPU performance on the vm, to be mor specific, here's a new screenshot running only the Windows VM in idle, also the proxmox is running a vztop:

there it shows that in Windows there's only 3% of the CPU being used, and in the proxmox shows 27%. We have seen this behaviour while the VM was in activity also. To have a little more data about it i've decided to run a benchmark software on the VM in the 1st thing that caught my attention was the CPU speed:

It shows that the CPU has only 366Mhz of speed wich is really low compared to the real speed of the processor. Another thing that is strange; the VM has 5000 CPU Units assigned of a 618000 total, but if i run a stability test, the 4 cores on the proxmox gets to 100% usage, if i didn't misunderstood the CPU Units option, it shouldn't be that way, i mean the use of the CPU should be limited, right?

 

[spirit]

Hi,
CPU Units don't work currently if you have a virtio devices in the qemu guest vm. (This will be fixed in proxmox 4.0, this is a limitation with current openvz kernel cpu scheduler).

About difference between host and inside guest cpu, this is because qemu process can use a lof of cpus for other things, mainly ios virtualisation (network, disk) and also interrupts/syscall from guest.

For example in windows, if you install sqlserver, it'll by default send a lot of interrupts at high rate.
https://pve.proxmox.com/wiki/Performance_Tweaks#Trace_Flag_T8038.

In proxmox 4.0, we have added some more hyper-v features, to reduce that with windows vm.


What software do you have installed inside the windows vm ?

 

[Martin Ezequiel]

Hi spirit thanks for your help. Currently there is installed a MySql database on the Windows, and when is in activity it has a lot of movement, and queries executing, so it would make sense if there is an issue with the system interrupts. Do you have some advices to increase performance on this subject?, or maybe it would be better to install MySql directly on Proxmox?

Also i still don't understand why is AIDA 64 showing me that the speed of the CPU is 366 MHz per core, is that right or normal?. I've been running a stability test with the AIDA soft, and it reached only 800MHz of speed, that is a little disappointing.

 

[spirit]

Hi spirit thanks for your help. Currently there is installed a MySql database on the Windows, and when is in activity it has a lot of movement, and queries executing, so it would make sense if there is an issue with the system interrupts. Do you have some advices to increase performance on this subject?, or maybe it would be better to install MySql directly on Proxmox?

just install mysql on a linux vm. Windows always have more overhead than linux currently.

[/QUOTE]
Also i still don't understand why is AIDA 64 showing me that the speed of the CPU is 366 MHz per core, is that right or normal?. I've been running a stability test with the AIDA soft, and it reached only 800MHz of speed, that is a little disappointing.[/QUOTE]
so known how it's work sorry.

 

[Martin Ezequiel]

Thanks for the recommendation. Going back to the processor, the vm has a 10% of the real capability of the processor, is there no way to increase that?. I need to virtualize only 3 VMs on Proxmox, and Windows should get most of the physical resources, buy if i can't get at least a little more of the CPU to the Windows, i'll be in some trouble. do i have a way to increase the CPU Resources on Windows?

 

[spirit]

Going back to the processor, the vm has a 10% of the real capability of the processor, is there no way to increase that

this is strange, with vt-x extension, you should have near 100% real capability.
which virtual cpu model do you have choose ? default kvm64 ?
if yes, maybe can you try to choose the cpu model matching your physical processor model.
This will enable advanced cpu flags, maybe AIDA64 is testing them.

 

[Martin Ezequiel]

I'm using 'host' CPU Model, so in the vm i see the physical processor model correctly, but the core speed is far smaller than its origilnal, in fact when i ran the AIDA tests on the VM the core speed didn't get much more than 600MHz. In this cap it shows the model and the speed

And this is the max speed i could get on a test:

 

[elkato]

Hi Martin,
have you already found any solution to your problem?
have you test with Win2008 server instead of Win2012?
We have some Win2008 on our Proxmox, and I could make some test with AIDA64 if you want... let me know.