Kvm io-performance with smp


#1

Hello,
i hope this topic isn’t discuss several times before but i found no similiar posting with the search-function.
I use kvm with proxmox ve and kvm work very well, but the io-performance with windows-guests is only good with one (guest)cpu.
The testings are based on kvm 0.12.3 (with the same result on 0.11.1).

Here is my posting, that i post in the proxmox-forum. But nobody has a solution there.

Hi,
after a lot more tests (on another node, with faster raid and the raid only for the vm)…
It seems that the IO-performance under windows with smp depends on fortune (or luck, or what else). If only run the IO-Prozess the values are sometimes not so bad, but if there another process, like the task-manager to show the cpu usage, the io-performance be worse. Up to very worse. I’ve got a notion that the performance drop if the io-process change the cpu (often).
It’s happens with the 2.6.32 and also with the 2.6.24 kernel (I don’t test the 2.6.18 yet).

Here the test-results (h2benchw -p -w 2cp_th_2.6.32_v1 2; profile install) on a virtio-disk (virtio-driver 4.3.0.17241) :
all values MB/s - different runs seperate with “|”

1 CPU 2.6.32: 488 1 CPU aio=threads 2.6.32: 517 | 573 | 569 2 CPU aio=threads 2.6.32: 333 | 78 | 28 2 CPU aio=native 2.6.32: 101 | 128 | 53 2 CPU aio=threads 2.6.32: 215 | 66 | 103 | 179 | 26 | 58 | 109 2 CPU aio=native 2.6.32: 70 | 39 | 3.7| 14 2 CPU aio=threads 2.6.24: 298 | 47 | 27 | 121 | 120 | 82 | 104 2 CPU cache=none 2.6.24: 55 | 92 | 102 | 114 | open task-manager: 67

Perhaps there are other switches for kvm to solve this problem?
My test kvm:

I will be quite happy, if someone has a hint for me.

Udo


#2

I think you will also no solutions from here :lol: