Re: Unpredictable performance degradation in QEMU KVMs

[Frantisek Rysanek]

...I forgot to mention CPU temperatures and frequencies.
When overheating, modern CPU's try to limit power consumption by 
throttling the clock rate.

The temperatures can be read at the cmdline from /sys/class/hwmon, 
provided that you have the right drivers loaded (for Intel CPU's I'd 
say "modprobe coretemp"). Not sure about the turbo frequencies, but 
while looking for details, I've found out that the "sysstat" package 
apparently has some very nice tools for that - namely, take a look at 
what data the "sar" tool can collect:
https://github.com/sysstat/sysstat

Frank