On Wednesday, 12/09/2009 at 08:20 EST, "Don W." <[email protected]> wrote: > When you set up the directory entry for a z/OS guest with multiple virtual > CPU's (e.g. CPU 00, CPU 01) and you QUERY CPUS, CPU 00 shows as BASE. What > is the difference between a BASE CPU and a non-BASE CPU? Does it really make > any difference in this environment. In terms of real processors, at one time > the base processor had to do the I/O. I do not believe that is true any > more. Am I correct? and when did that stop being the case?
The "base" CPU is the first CPU that is defined to your virtual machine. What it really means is that you can't DETACH it, since every virtual machine must have at least one virtual CPU. Otherwise the term is meaningless. Each processor has always been able to do its own I/O. What changed (370 -> XA) was the introduction of a "channel subsystem" that enabled any processor to get to any device. Prior to that, each CPU had its own set of channels. I/O to *that* device had to be scheduled on *that* CPU. Now we're all one happy family! Alan Altmark z/VM Development IBM Endicott
