On Thursday, 08/28/2008 at 12:00 EDT, Kris Buelens <[EMAIL PROTECTED]> wrote: > Linux guests under secondlevel z/VM would incurr high CPU overhead, > 50% for example. The current z series supports 2 layers of > virtualization. LPAR uses the first layer, a z/VM guest the second. > These days a secondlevel z/VM is in fact 3'th level, what means > simulation.
Actually, it's part hardware and part simulation. An "nth" level SIE instruction will "pancake" down. By this I mean that if the Interpretive Execution Facility is not available, the SIE is trapped by the invisible CP underneath and modified in a way that represents a "more real" view of that nth level guest. The Pancake Effect continues until you hit the Interpretive Execution Facility where real SIE is used to run the guest, not just SIE running a SIE simulation. There are some things that "break off" during the pancake process and those parts are simulated. Alan Altmark z/VM Development IBM Endicott
