13501ADC@MSU.BITNET ("Alan D. Cabrera") (07/09/87)
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? Alan D. Cabrera BITNET: 13501ADC@MSU Computer Laboratory 400D Computer Center Michigan State University East Lansing, MI 48824
oberman@LLL-ICDC.ARPA ("Oberman, Kevin") (07/10/87)
>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. ------
helen@uhccux.UUCP (Helen Rapozo) (07/15/87)
In article <8707110202.AA28088@ucbvax.Berkeley.EDU>, 13501ADC@MSU.BITNET ("Alan D. Cabrera") writes: > > 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? The only reason why a job running at priority 1 is executing is because the other process on the system that have priority 2 to 31 is not using the CPU in the first place. If you think about the NULL process runs at priority 0 so if the system is not doing anything else it will execute that process which happens to be an infinite loop. If this job that runs at priority 1 is doing useful work then the system is doing more useful work. Seriously tho, since the job pages a lot that could explain the degredation in response time. You could do the following things: a) Run the job at priority 0. What will happen is that whatever CPU cycles that are left will be split between NULL and your process. b) Somehow get a bigger working size for your job, the less paging you do the faster things will go. c) If you are the system manager there is a parameter that deals with the timeslice, if you decrease the timeslice the effect to the users will be one of faster response time. Let me know how this turns out.