Comment 8 for bug 1481272

I have experienced this behavior (main-loop: WARNING: I/O thread spun for 1000 iterations) and the resulting degraded performance. The VM becomes very unresponsive but eventually recovers. My setup:

Ubuntu 15.10 | qemu-system-x86_64 --version QEMU emulator version 2.3.0 (Debian 1:2.3+dfsg-5ubuntu9)
HW = Dell Precision M6600 with Intel(R) Core(TM) i7-2760QM CPU

I agree with other comments that it seems related to high disk I/O as the problem seems to occur during VM install or other VM operations which read/write large amounts of data.