[Qemu-discuss] Guest has high iowait cpu usage but HV has no iowait

[Chengyuan Li]

Hi,

I'm running a high I/O bound application in the KVM/QEMU VM, and I can see high %wa cpu usage in the guest.

%Cpu(s): 14.5 us, 11.3 sy,  0.0 ni, 36.2 id, 37.0 wa,  1.0 hi,  0.0 si,  0.0 st

But %wa in the HV is always 0. 

%Cpu(s):  9.4 us,  1.5 sy,  0.0 ni, 89.0 id,  0.0 wa,  0.0 hi,  0.1 si,  0.0 st

My understanding is that VM's disk I/O is done by QEMU's I/O threads in HV, and running iostat in HV can also see heavy disk throughput, but why HV's %wa  is 0 always ? 

Regards,

CY.