kvm io-performance with smp

[Udo Lembke <ulembke@polarzone.de>]

Hello,
i'm new on this list and hope this topic isn't discuss several times before.
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 there 
know a solution.

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 "|"

<http://forums.meulie.net/viewtopic.php?f=43&t=6136&sid=79fe2173580718169824cb2e454a3efa#>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:|
/usr/bin/kvm -monitor unix:/var/run/qemu-server/126.mon,server,nowait 
-vnc unix:/var/run/qemu-server/126.vnc,password -pidfile 
/var/run/qemu-server/126.pid -daemonize -usbdevice tablet -name knecht2 
-smp sockets=2,cores=1 -nodefaults -boot menu=on,order=c -vga cirrus 
-tdf -localtime -rtc-td-hack -k de -drive 
file=/var/lib/vz/template/iso/vm-tools.iso,if=ide,index=1,media=cdrom 
-drive 
file=/var/lib/vz/images/126/vm-126-disk-1.raw,if=ide,index=0,boot=on 
-drive file=/var/lib/vz/images/126/vm-126-disk-2.raw,if=ide,index=2 
-drive 
file=/var/lib/vz/images/126/vm-126-disk-3.raw,if=virtio,index=0,aio=threads 
-m 1024 -net 
tap,vlan=0,ifname=vmtab126i0,script=/var/lib/qemu-server/bridge-vlan 
-net nic,vlan=0,model=e1000,macaddr=F6:E1:E2:E4:93:4E|

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

Best regards

Udo