Date: Mon, 26 Jan 2004 12:01:30 +1100 From: Peter Jeremy <peterjeremy@optushome.com.au> To: Andy Farkas <andyf@speednet.com.au> Cc: freebsd-current@freebsd.org Subject: Re: 80386 support in -current Message-ID: <20040126010130.GA45948@server.vk2pj.dyndns.org> In-Reply-To: <20040126072708.Y72566@hewey.af.speednet.com.au> References: <20040124074052.GA12597@cirb503493.alcatel.com.au> <xzpptd9qsf0.fsf@dwp.des.no> <20040125143203.G29442@gamplex.bde.org> <20040125195224.GA45925@server.vk2pj.dyndns.org> <20040126072708.Y72566@hewey.af.speednet.com.au>
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On Mon, Jan 26, 2004 at 07:37:48AM +1000, Andy Farkas wrote: >Peter Jeremy wrote: > >> Interesting. Does anyone on this list actually use -CURRENT on a 386? >... >> >> Is it time to bite the bullet and fully desupport the 80386? It looks >> like threads don't work and it's likely that other bitrot will set in >> in the absence of active testing. > >Yes. Bring on the axes! > >This came up almost a year ago (late Feb 2003). Here are some exerps from >a few emails I kept on the subject: I remember one thread on this subject but don't recall if it was that one. As I recall, the agreed outcome went something like drop 80386 support from GENERIC but retain it primarily for embedded applications. >%%% >Poul-Henning Kamp <phk@FreeBSD.ORG> wrote: > >My main concern would be if the chips have the necessary "umphf" >to actually do a real-world job once they're done running all the >overhead of 5.0-R. The lack of cmpxchg8 makes the locking horribly >expensive. >%%% Note that cmpxchg8 doesn't exist in 486 either and is only necessary to support 8-byte atomic operations - I may be wrong but it should be possible to handle i386 locking with only 4-byte operations. Of course, the 80386 doesn't have cmpxchg either, which _does_ make locking horrible (requires sti/cli which doesn't work in the multi- master case). >This last point is the clincher. The chip does NOT have enough "umphf". I >actually managed to boot a -current (from back then) on a 80386SX and it >was torturously slow. An ls(1) on my empty home directory took 15 seconds. >My VAX is faster. This is a bug in FreeBSD 5.x - the performance in general has degraded since 4.x. Performance degradation is often more obvious in lower end machines. Peter
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