Date: Fri, 18 Apr 1997 08:56:33 +0100 From: Bob Bishop <rb@gid.co.uk> To: KATO Takenori <kato@eclogite.eps.nagoya-u.ac.jp> Cc: freebsd-bugs@freefall.freebsd.org Subject: Re: kern/3292: Cyrix 486 performance problem Message-ID: <l03020901af7cd2bf56c0@[194.32.164.2]> In-Reply-To: <199704180204.LAA03835@gneiss.eps.nagoya-u.ac.jp> References: Your message of "Thu, 17 Apr 1997 15:40:02 -0700 (PDT)" <199704172240.PAA11576@freefall.freebsd.org>
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At 3:04 am +0100 18/4/97, KATO Takenori wrote: >To determine cache disable/enable by default is to determine support >all/not-all Cx486 box. If CPU cache is enabled by default, FreeBSD >cannot boot on old Cyrix-unaware motherboards. > >Because Cyrix sold 486SLC/DLC series as `up-grade products', I >considered that FreeBSD should support old motherboard users and >disable CPU cache by default[etc] Have we actually had many (any?) complaints from Cx486 users about this? Consider the possibilities: if it won't run FreeBSD with the cache enabled, then either: a) It won't run DOS either - motherboard just too broken b) It runs DOS but slow - BIOS doesn't know how to initialise the chip. AFAIK DOS contains no Cyrix-specific initialisation code. c) It runs DOS at full speed - (i) something is broken that FreeBSD needs but DOS doesn't, or (ii) FreeBSD initialisation code is broken. In case (c)(ii) we should fix the code. Case (c)(i) is not very likely and we can do nothing about. Case (b) is unlikely too - user would not accept an 'upgrade' that does not improve performance! Case (a) no-one should expect FreeBSD to run anyway. Bottom line: if the machine runs DOS properly, I don't think it is very risky to enable the cache. If it doesn't run DOS properly, then we should not expect it to run FreeBSD. BUT in any case, I think the cache should be enabled by default. If that means implementing cache flush code, so be it. We can't get to a release where all Cx486 run like a dog with the GENERIC kernel: instead of complaints from a few users with old motherboards, we will upset all users (maybe many of them) who are currently running at full speed with Cx486. -- Bob Bishop (0118) 977 4017 international code +44 118 rb@gid.co.uk fax (0118) 989 4254 between 0800 and 1800 UK
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