Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!mailrus!tut.cis.ohio-state.edu!ucbvax!UOTTAWA.BITNET!451061 From: 451061@UOTTAWA.BITNET (Valentin Pepelea) Newsgroups: comp.sys.amiga.tech Subject: Re: Address Spaces (was Re: (Fairly) Complete Amiga VM design) Message-ID: <8906192229.AA21151@jade.berkeley.edu> Date: 19 Jun 89 21:51:25 GMT Sender: daemon@ucbvax.BERKELEY.EDU Lines: 35 Dave Haynie writes in message <7096@cbmvax.UUCP> > For a 16 meg system you have 128 table entires, and > so will occasionally have an ATC miss, though I'm not sure this could > actually be noticed (The MMU will find the page entry very quickly, since > except for CARDROM translations it's only a 1-level page table). The size of the 128 pages that you use is irrelevant, since the MMU will store in the ATC one entry for each page, where the page size is stored in the PS field of the TC register. In SetCPU 1.4 you use a rather wierd TC setup, where the pagesize is 4K. That means that there is an ATC entry for each 4K page, right? Wrong! The ATC stores page descriptors also according to function codes, wether you use them or not. In other words, you get a lot more ATC misses then you thought, eh? So if you want to improve a little your ATC hit ratio, simply rearrange your TC register to use 32K pages. Thus the hit ratio will improve by 1/exp(32/4). Pretty good tip, eh? > The 68030 has a smaller ATC, What I said holds true for the 68851. I just bought the 68030 manual, and will soon be able to tell what best goes for it. >Dave Haynie "The 32 Bit Guy" Commodore-Amiga "The Crew That Never Rests" Valentin _________________________________________________________________________ "An operating system without Name: Valentin Pepelea virtual memory is an operating Phonet: (613) 231-7476 (New!) system without virtue." Bitnet: 451061@Uottawa.bitnet Usenet: Use cunyvm.cuny.edu gate - Ancient Inca Proverb Planet: 451061@acadvm1.UOttawa.CA