Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!seismo!husc6!mit-eddie!ll-xn!cit-vax!ucla-cs!zen!ucbvax!LLL-ICDC.ARPA!oberman From: oberman@LLL-ICDC.ARPA ("Oberman, Kevin") Newsgroups: comp.os.vms Subject: RE: Running images at priority 1 Message-ID: <8707110525.AA01423@ucbvax.Berkeley.EDU> Date: Fri, 10-Jul-87 10:48:00 EDT Article-I.D.: ucbvax.8707110525.AA01423 Posted: Fri Jul 10 10:48:00 1987 Date-Received: Sun, 12-Jul-87 14:23:07 EDT Sender: daemon@ucbvax.BERKELEY.EDU Reply-To: "Oberman, Kevin"Distribution: world Organization: The ARPA Internet Lines: 33 >I've been submitting CPU intensive batch jobs on our VAX 8650 with the priority >set at 1. It uses some pretty big arrays so it tends to page ALOT. When I run >my job people say that they notice a degredation to the system. I say that my >job shouldn't pose a problem because it's priority is lower than theirs. >Am I wrong in assumming that since my job's priority is set at 1, it shouldn't >interfere with anybody with a higher priority? This seems to pop up fairly regularly. Yes, you are wrong. I once looked at all of the gory details, but even a low priority process competes with higher priority processes for many resources besides CPU cycles. The process priority has no effect on these. In your case I suspect that you are using a fair amount of virtual address space which, in turn, requires lots of paging and, probably, a big chunk of physical memory for the working set. Because memory management is handled by the system kernal, outside of the normal process context, the fact that the process is running at a low priority makes no difference. A low priority job may not get many CPU strokes for the user-mode code, but if it gets enough to cause paging, it can start impacting the system in a very noticable way. R. Kevin Oberman Lawrence Livermore National Laboratory arpa: oberman@lll-icdc.arpa (415) 422-6955 Disclaimer: Neither my employer nor myself can take resposibility for the accuracy of this information. I believe it is correct, but if it's not I can only say "Sorry". I'm a rotten typist and a worse speller, so forgive any silly errors. ------