Path: utzoo!attcan!uunet!husc6!mailrus!ames!umd5!brl-adm!adm!weiser.pa@xerox.com From: weiser.pa@xerox.com Newsgroups: comp.unix.wizards Subject: Re: Vax 11/780 performance vs Sun 4/280 performance Message-ID: <15464@brl-adm.ARPA> Date: 31 May 88 19:36:40 GMT Sender: news@brl-adm.ARPA Lines: 41 -------------------- Nonsense, I just tried forking 32 copies of the following program on my Sun 3/60 workstation. Each one sleeps for 100 milliseconds, wakes up, and sleeps again. With 32 copies of it running, I could notice no difference in response time and a `ps aux' showed none of them using a significant amount of CPU time. Maybe you are just running out of memory and doing alot of swapping? What I have noticed on our Vax 11/780, running VMS, is that it is often equally slow with 1 user or 20 users. Possibly VMS avoids the `knee' by raising the priority of the NULL task when there aren't many people on the machine??? #includemain() { struct timeval tv; tv.tv_sec = 0; tv.tv_usec = 100000; for( ;; ) select( 0, 0, 0, 0, &tv ); } -------------------- No, not nonsense. I changed 100000 to 25000, and ran 18 of these on my Sun-4/260 with 120MB swap and 24MB ram, with very little else going on. Perfmeter shows no disk activity, ps aux shows each of the 18 using almost no cpu. (And each of the 18 has more than millisecond to get in and out of select, which is certainly enough). And the system is to its knees! (If it doesn't work for you, try 19 or 20 or 21). Window refreshes take 10's of seconds. If I kill off 3 of these, all is back to normal. I don't have a 60C to try this on. But, try reducing that delay factor and see if you don't also see a knee in the performance curve well before the cpu should be swamped. (And in any case, swamped cpu doesn't need to imply knee in the curve...) -mark