qemu -enable-kvm *slower* than pure emulation for x86

Well it turns out that issue is the clock source used by kvm on the host system. Have a look at the output of:

$ cat /sys/devices/system/clocksource/clocksource0/current_clocksource

if it's tcs or tcs_early you have found the culprit, change it to one of the other available clock sources on your system:

$ cat /sys/devices/system/clocksource/clocksource0/available_clocksource

For example hpet (high performance event timer):

$ echo hpet | sudo tee /sys/devices/system/clocksource/clocksource0/current_clocksource

Ahmed Masud

Posted 2018-04-28T05:19:52.883

Reputation: 424

Any chance of an explanation of why tcs is a bad clock source to use compared to others? Are there any other downsides or benefits to changing the clock source? – Mokubai – 2018-04-28T07:51:53.357

Possible information on the why from Intel (https://software.intel.com/en-us/blogs/2013/06/20/eliminate-the-dreaded-clocksource-is-unstable-message-switch-to-tsc-for-a-stable) but I'm not convinced as it mentions the Xeon Phi as problematic and not supporting invariant tsc.

– Mokubai – 2018-04-28T08:05:29.863

1I didn't get into figuring out why tcs clock is a bad source, just didn't have the time to go around hacking kvm code. I'll probably run some tests after the silly project that I have going gets done. However it's definitely the culprit, because the problem is easily reproduced on multiple hardwares with several permutations – Ahmed Masud – 2018-04-28T16:09:02.007

qemu -enable-kvm slower than pure emulation for x86_64

Answers

qemu -enable-kvm *slower* than pure emulation for x86_64

Answers

qemu -enable-kvm slower than pure emulation for x86_64