Don't bother defining more than 1 to a machine that just runs a Multitasking CMS application - it actually slows things down due to the fact that most system calls switch back to the base processor.
-----Original Message----- From: The IBM z/VM Operating System [mailto:[EMAIL PROTECTED] On Behalf Of Adam Thornton Sent: Thursday, 14 February 2008 11:58 AM To: IBMVM@LISTSERV.UARK.EDU Subject: Re: To define virtual processors or not On Feb 13, 2008, at 6:54 PM, Paul Vincent wrote: > Hello List, > > I'm new to z/VM and have a question. Should I define virtual > processors to > z/VM service ids/guests (TCPIP, Linux guests...) with the 'MACHINE > ESA ## & > CPU #' control statements in the USER DIRECT file? Is there a > performance > benefit/cost, if I have more than 1 IFL, to define virtual > processors equal > to the number of IFLs? Or will a single virtual processor perform > just > fine. I like defining two (assuming that my real load is less than two full engines' worth) or as-many-as-I-expect-to-be-able-to-use-if-more-than- two. Basically, this is to give my workload the best chance of parallel dispatch. If I only have one virtual processor, I only have one thing *really* going on at a time in my Linux guest, even if the actual work is hopping around real processors. I don't have any hard data that tells me this is really working, though. Does anyone? Adam
