On 02/10/2016 01:50 PM, Tony Harminc wrote: > 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. > > Well that was sort of my first thought too, but the actual wording in z/VM Statement of Direction was that "the IBM z13 server family will be the last to support ESA/390 architecture mode", not that it wouldn't support ESA/390 mode on IPL. That sure sounds like there will no longer be any hardware ability to switch ARCHLVL mode, and that z14 and later will run only in ARCHLVL2 mode.
-- Joel C. Ewing, Bentonville, AR [email protected] ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
