On 10 February 2016 at 13:33, Joel C. Ewing <[email protected]> wrote: > Now I see the light -- had forgotten about the whole ARCHLVL-mode > switch thing going on under the covers.
This switch is made only once, remember. It's slow, and it affects all the CPUs in the configuration. > This effectively also rules out > the possibility of any z/VM on a z14 or later being able to provide > ESA/390 support to any Virtual Machine as well, since there many > significant differences (register sizes, prefix area, privileged > instructions behavior, etc) when running z/Architecture mode, and with > CP's in that mode the only way to achieve ESA/390 behavior when the > hardware no longer supports it would be grossly inefficient emulation. Why do you think that SIE would not continue to provide virtual ESA/390 support? Today, when z/VM is running in zArch mode on the metal on e.g. a z12, it can surely have an ESA/390 mode guest OS. I see no reason that wouldn't continue just because the host processor doesn't IPL in ESA/390 mode. Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
