So it appears the LGR facility to limit the instruction set is not
practical for those ISVs who wish to test thei software on prior
generations of z hardware, since they probably don't have the hardware
farm (unless LGR works on a couple of zPDTs hooked together).
Gary Weinhold
On 2019-03-27 9:57 a.m., Tony Thigpen wrote:
My understanding is that it is automatic when you are VM guest, and
you can't LRG unless you are a guest, so z/OS (if it supported LGR)
does not have to do anything.
Tony Thigpen
Peter Relson wrote on 3/27/19 9:32 AM:
<snip>
When a z/VM guest issues the STFLE command, z/VM intercepts it and
returns the lowest-common-denominator value for all processors available
for LGR.
</snip>
I think this implies that any user of LGR must have "pre-set" the
definition of "processors available for LGR" before IPLing an image
(such
as z/OS). If that's the expectation and the reality, then I agree.
I was
thinking of some change "after IPL", but perhaps that is what cannot
happen.
For example, if you have a z14 but have defined a rule such as "I might
want to use LGR down to a z13" and that rule gets applied to an IPLing
z/OS, then only the z13 facilities would show up. Can there be such a
(hypothetical) definition set up for each individual guest, as
opposed to
there being one definition for all guests (the latter seeming far too
restrictive)?
Peter Relson
z/OS Core Technology Design
Gary Weinhold
Senior Application Architect
DATAKINETICS | Data Performance & Optimization
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