Calculate the CPI for the system listed above assuming that there are no accesses to I/O. What is the CPI if the VMM performance impact doubles? If it is cut in half? If a virtual machine software company wishes to obtain a 10% performance degradation, what is the longest possible penalty to trap to the VMM?

One of the biggest impediments to widespread use of virtual machines is the performance overhead incurred by running a virtual machine. The table below lists various performance parameters and application behavior.

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a. b. Base CPI 1.5 1.75 Priviliged 0/S Accesses per 10,000 Instructions 120 90 Performance Impact to Trap to the Guest O/S 15 cycles 20 cycles Performance Impact to Trap to VMM 175 cycles 140 cycles 1/0 Accesses per 10,000 Instructions 30 25 1/0 Access Time (Includes Time to Trap to Guest 0/S) 1100 cycles 1200 cycles