Bad Network Performance with KVM Guests

[dietmar]

I only can use 3,23Gbits of 10Gbits. I use the virtio driver for all of my vms, but I have also tried to use the e1000 nic device instead.

With starting the iperf performance test on multiple vms simultaneously I can use the full bandwidth of the kvm host's interface. But only one vm can't use the full bandwith. Is this a known limitation, or can I improve this performance?

The CPU overhead for IO is currently a bit too high - So I guess the CPU goes to 100% (for one CPU) when your run those IO tests?

 

[rscholte]

actually I have no problems with usage of my cpu during this tests.
Not on the kvm-host and not inside the guest:

KVM-Guest
top - 08:50:55 up 11:25, 1 user, load average: 0.43, 0.14, 0.05
Tasks: 81 total, 1 running, 80 sleeping, 0 stopped, 0 zombie
Cpu0 : 0.1%us, 0.4%sy, 0.0%ni, 98.5%id, 0.8%wa, 0.0%hi, 0.1%si, 0.0%st
Cpu1 : 0.2%us, 0.4%sy, 0.0%ni, 99.3%id, 0.0%wa, 0.0%hi, 0.1%si, 0.0%st
Mem: 1023532k total, 597276k used, 426256k free, 70772k buffers
Swap: 1049592k total, 0k used, 1049592k free, 447928k cached


KVM-Host
Tasks: 319 total, 1 running, 318 sleeping, 0 stopped, 0 zombie
Cpu0 : 9.6%us, 9.9%sy, 0.0%ni, 64.2%id, 0.0%wa, 0.0%hi, 16.2%si, 0.0%st
Cpu1 : 6.4%us, 12.4%sy, 0.0%ni, 63.0%id, 0.3%wa, 0.0%hi, 17.9%si, 0.0%st
Cpu2 : 4.6%us, 2.3%sy, 0.0%ni, 92.8%id, 0.0%wa, 0.0%hi, 0.3%si, 0.0%st
Cpu3 : 4.3%us, 3.0%sy, 0.0%ni, 92.1%id, 0.0%wa, 0.0%hi, 0.7%si, 0.0%st
Cpu4 : 0.3%us, 3.3%sy, 0.0%ni, 95.4%id, 0.0%wa, 0.0%hi, 1.0%si, 0.0%st
Cpu5 : 1.0%us, 0.3%sy, 0.0%ni, 98.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu6 : 0.4%us, 1.6%sy, 0.0%ni, 97.5%id, 0.0%wa, 0.0%hi, 0.4%si, 0.0%st
Cpu7 : 1.0%us, 1.3%sy, 0.0%ni, 97.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu8 : 0.0%us, 1.4%sy, 0.0%ni, 98.6%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu9 : 0.3%us, 3.9%sy, 0.0%ni, 95.8%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu10 : 0.7%us, 1.9%sy, 0.0%ni, 96.5%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu11 : 0.7%us, 0.7%sy, 0.0%ni, 98.7%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu12 : 1.3%us, 1.3%sy, 0.0%ni, 97.4%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu13 : 0.0%us, 0.0%sy, 0.0%ni,100.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu14 : 10.2%us, 1.1%sy, 0.0%ni, 88.6%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Cpu15 : 28.8%us, 5.1%sy, 0.0%ni, 66.0%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 33005428k total, 5292376k used, 27713052k free, 120588k buffers
Swap: 4194296k total, 0k used, 4194296k free, 828588k cached