Tom Schmidt <[EMAIL PROTECTED]> wrote: >I've been running VM more off than on since PLC 5 and I'm certain that the >behavior that I >referenced WAS in VM... at some point. But if you & Lynn Wheeler say it isn't >there now, >I'll believe you (unless/until I can prove you wrong, of course). >But I know back in the VM/HPO or (maybe) early VM/XA days it was true that VM >put itself >into a tiny loop while it waited for work. The loop was in a unique-to-VM PSW >key so that >the hardware monitor (the "speedometer") could tell the difference between >work and wait. >Or am I the only person who "remembers" that? No, you aren't. HPO 3.4 added "Active Wait", which was interesting enough that it was granted a patent (cf. http://www.freepatentsonline.com/4631674.html). Modern VMs use the TPZI instruction (Test Pending Zone Interrupts), which basically says "Mr. PR/SM, please wake me up when I have something to do". Without it, PR/SM wouldn't work real well. (ObAnecdote: there were plenty of DOS-based PC programs that polled -- typically for keyboard interrupts -- in a fashion conceptually similar to Active Wait, and were really poor citizens under Windows until cured.)
ISTR a brief period, before the unique PSW key (or perhaps simply before some then-current performance monitor knew about it), when it was impossible to tell how busy an HPO box really was. This entire discussion is interesting to a VMer. VM has always done VTIME and TTIME: VTIME is the CPU time used by the guest, TTIME is the VTIME plus CP overhead. VTIME should be repeatable independent of system load; TTIME is what varies. VMers talk about "T/V ratios", i.e., "How well are we doing in terms of overhead?" (Goal=1.00) ...phsiii ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
