Hi,
Each vCPU has its own TSC. A desirable property of such a system is that
the TSCs of all of the vCPUs in a VM are exactly synchronized.
If the TSCs are exactly synchronized, when software reads the TSC of vCPU A and then reads the TSC of vCPU B,
the read on B is guaranteed to be a larger value than the read on A. If the TSCs are not exactly synchronized,
this is not necessarily true.
Now in KVM, we can't guarantee all the vCPUs' TSC to be exactly synchronized,
Because we can't guarantee all vCPU threads to be scheduled in the same time after VM is starting.
The offset value of vCPUs' TSC will be worse when the pressure of host is large.
So is it necessary to sync all vCPUs' TSC when the guest start? May be we could set the tsc_offset to the same value,
when vCPU is created. Is it acceptable?
Thanks,
zhanghailiang
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