Added warning that the cycle count might not be stable.
Added warning that the cycle count might not be stable.

The cycle count is traditionally not stable between different cores, due
to frequency changes etc. OS might provide something which is more
stable but still accurate enough.

smarr/OmniVM,smarr/OmniVM,smarr/OmniVM,smarr/OmniVM,smarr/OmniVM,smarr/OmniVM,smarr/OmniVM,smarr/OmniVM