Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!thunder.mcrcim.mcgill.edu!snorkelwacker.mit.edu!usc!zaphod.mps.ohio-state.edu!van-bc!ubc-cs!alberta!cpsc.ucalgary.ca!deraadt From: deraadt@cpsc.ucalgary.ca (deraadt) Newsgroups: comp.arch Subject: Re: ~8-job "knee" in response curves on Suns (was Re: IBM RS6000) Message-ID: Date: 15 Jan 91 14:59:40 GMT References: <1991Jan10.214122.9506@news.arc.nasa.gov> <5257@auspex.auspex.com> Organization: UofC cpsc Lines: 42 In-Reply-To: guy@auspex.auspex.com's message of 15 Jan 91 18:45:57 GMT Nntp-Posting-Host: fsa In article <5257@auspex.auspex.com> guy@auspex.auspex.com (Guy Harris) writes: > >(This "ledge" at 8 processes is a feature of SUNOS, and appears on all > >Sun hardware). > > I suspect it's more a feature of the Sun MMU which has, on many > machines, 8 contexts, one of which is used by the kernel and the other 7 > of which are used for user-mode processes; if the job to which you're > switching contexts has a context in the MMU, you can switch address spaces > setting the context register, but otherwise, you have to find a free > context or steal one from another process and load up translations for > that process into that context. This is correct. > Some Sun hardware has more than 16 contexts, and some doesn't have > contexts at all - the Sun-3/80 and Sun-3/4xx have 68030s and use the 3/80 and 3/4xx have 030 in them, but the Sun MMU is used. The motorola MMU is never enabled. The 386i uses the Intel MMU though. > on-chip MMU, not a Sun MMU, and the Sun386i uses the on-chip MMU as well. All Sun4 hardware has at least 16. Sun4/4x0 have 64. > Have you seen this "knee" on Suns without a Sun MMU, and on machines > with a Sun MMU but more than 8 contexts, have you seen the knee at 8 or > so jobs? If not, I suspect it's MMU-related, not SunOS-related > ("SunOS", not "SUNOS", please; in Sun's name, "Sun" isn't an acronym). It is mmu related, but his knee should be higher. I saw the original posting, and was shocked to see that it did not mention which Sun had been tested. A lowely little 4/110 and a 4/490 certainly cannot be classed as giving the same performance.