On Tue, Nov 12, 2019 at 8:43 AM Tom Marchant < 000000a69b48f3bb-dmarc-requ...@listserv.uga.edu> wrote:
> >I cannot fathom the reason to use _any_ base for the PSA other than GPR0. > >It is simply wasteful of a scarce resource. > > It isn't "the" PSA. There is the PSA of the processor that you are running > on. > That PSA is always at location 0. > True. I left out the words "of the processor". I guess that I ASSuMEd that. > > Every processor in the LPAR has its own PSA, and when the processor is > running, > that PSA is at real (and virtual) location 0 for that processor. The PSA > for any > other processor can also be referenced using the real address that matches > the > value that is used for the prefix register for that processor. This is > documented > in the Principles of Operation under "Prefixing". > I know. But I have never wanted to look at the PSA of any CP other than the one that I am running on. I'm not really sure why I would. Do you know of a reason to do so? I am curious. > > You cannot use the value in the prefix register for your own processor to > reference > your PSA though. That would get you to absolute page 0, which, if I > understand > correctly, MVS never uses. > That's interesting. So z/OS and it's ancestors have never really used absolute page 0. I guess it doesn't really matter since it is a small amount of physical storage in today's world. Actually, I thought absolute 0 was used as the PSA for the IPL processor, but that, again, was an assumption. > > -- > Tom Marchant > -- People in sleeping bags are the soft tacos of the bear world. Maranatha! <>< John McKown
