I would have thought that a directory entry of some sort would have been the choice - a "if it isn't in the directory, it can't be done" sort of thing. The DEFINE is class G meaning anybody can do it at any time, even though they do not know what they are doing. (I am sure nobody would ever think of defining the CPU as an IFL, IPLing CMS and running a tight CPU loop. Certainly there would never be more than one of these at the same time.)
Regards, Richard Schuh > -----Original Message----- > From: The IBM z/VM Operating System > [mailto:ib...@listserv.uark.edu] On Behalf Of Alan Altmark > Sent: Thursday, August 20, 2009 6:28 AM > To: IBMVM@LISTSERV.UARK.EDU > Subject: Re: z/VM mode LPARs > > On Thursday, 08/20/2009 at 07:28 EDT, Michael Coffin > <michaelcof...@mccci.com> wrote: > > I actually scoured the z/VM 5.4 doc looking for a > documented method of > > doing this, but did not find anything specific. I had assumed it > > would probably be the CPU directory record that we would use to do > > this, but that did not turn out to be the case. > > Now that we have the COMMAND statement, there is no longer a > compelling reason to add or change directory statements if > there is a SET or DEFINE command to alter the virtual machine > configuration. Most changes will be in the OPTIONS statement. > > COMMAND SET and COMMAND DEFINE is precisely the way we > intended you to configure such guests. See the DEFINE CPU > command for details on knowing when you need SET VCONFIG > and/or the TYPE option on DEFINE CPU. > > > PS: Yes, we've given each Linux server 5 virtual CPU's, > which map to > > two real IFLs. Our thinking on this is that the Linux > guest "should" > > dispatch more work simultaneously with 5 CPU's (and the two > real IFLs > > can more than handle the load). Comments? Good idea/bad idea? > > Having more virtual CPUs does not give the guest more access > to the CPU; it is SET SHARE that does that. In general, the > number of virtual CPUs should not exceed the number of > logical CPUs that CP has at his disposal. > In your configuration, each vCPU has 1/5 of the virtual > machine's SHARE value and three of the five vCPUs *must* wait > at any given time. But don't take this a "that's all there > is" because Linux can manage idle CPUs in a way that avoids > the "1/5" effect. However, you still will want to observe > the "virtual/logical CPU <= 1" ratio unless you have > measurements that justify > 1. > > And, as Rob says, you actually need an application that > *effectively* uses multiple virtual CPUs. > > Alan Altmark > z/VM Development > IBM Endicott >
