Paravirtualized KVM clock

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Paravirtualized KVM clock

Avi Cohen
My name is Avi Cohen and I work in toganetworks which is part of Huawei ERC.

1.       My VM is  Fedora 21 and the host is Fedora 22 (kernels are 4.1 and 4.2 accordingly)

2.       My Intel core processor  supports  the constant-tsc.

3.       The default clock in the guest is kvm-clock .
When I run a test to  measure packet delay between the host and the VM  (which normally  should be  about 5  to 10 micro-sec) - I see about 800 mili-sec delay
I see that delta time between the VM and host is about 800ms  - which means that the sync. Accuracy is bad
What accuracy do I have to expect with this clocking mode (kvm-clock) ?  tens of ms/us/ns?
Maybe I've missed some configuration to achieve a better accuracy ?
Thanks and Regards,

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