Date: Wed, 24 May 2000 09:28:16 -0600 From: Steve Passe <smp@timing.com> To: Chuck Paterson <cp@bsdi.com> Cc: arch@FreeBSD.ORG Subject: Re: Preemptive kernel on older X86 hardware Message-ID: <200005241528.JAA23192@Ilsa.StevesCafe.com> In-Reply-To: Your message of "Wed, 24 May 2000 08:46:03 MDT." <200005241446.IAA05589@berserker.bsdi.com>
next in thread | previous in thread | raw e-mail | index | archive | help
Hi, > The 386 processors do not support the locked exchange instruction. > For these systems the locked exchange can be replaced with roughly > a "cli, tst, cmp, branch, store, sti". > > The following are the obvious choices ... > 3) Drop support for 386. We could live with this, but I suspect there are others depending on 386EX type solutions. > Neither the 386 nor the 486 have a processor priority register or > cycle counters. Currently the BSD/OS SMPng kernel requires both of ... > The argument, within BSDI, for supporting the older stuff is that > new embedded systems are being built with these processors. Raw > chip cost being the reason. While I believe the person telling me > this, I haven't personally seen the evidence, I haven't looked > either. The majority of systems we ship today use 486 class CPUs. The real work gets done on pentium (ie 586) class CPUs, but for each of these there are up to 5-6 "distribution" systems that use a FreeBSD/486 system to monitor system health, etc. The 486 boards are plentiful (and cheaper) in the "embedded" world. > I have talked to a couple of people who think that supporting this > older stuff won't be important to FreeBSD by the time the kernel > is preemptive. Some even thought supporting the original Pentium > processors might not be required. I'll propose the following as it > reduces the work required: > > > Once FreeBSD has a preemptive kernel FreeBSD will only run on > Pentium or better X86 processors. > > > I'm not wed to the above at all, it is more to get discussion > started than anything else. Then again, if no one complains, it is > easier. We would have no need for SMP on 486 or 586, however losing UP on 486 would be a problem. -- Steve Passe | powered by smp@timing.com | Symmetric MultiProcessor FreeBSD To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200005241528.JAA23192>