From owner-freebsd-hackers Sat Jan 13 16:36:25 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.3/8.7.3) id QAA29790 for hackers-outgoing; Sat, 13 Jan 1996 16:36:25 -0800 (PST) Received: from phaeton.artisoft.com (phaeton.Artisoft.COM [198.17.250.211]) by freefall.freebsd.org (8.7.3/8.7.3) with SMTP id QAA29780 for ; Sat, 13 Jan 1996 16:36:22 -0800 (PST) Received: (from terry@localhost) by phaeton.artisoft.com (8.6.11/8.6.9) id RAA24502; Sat, 13 Jan 1996 17:29:50 -0700 From: Terry Lambert Message-Id: <199601140029.RAA24502@phaeton.artisoft.com> Subject: Re: X for install To: msmith@atrad.adelaide.edu.au (Michael Smith) Date: Sat, 13 Jan 1996 17:29:50 -0700 (MST) Cc: terry@lambert.org, msmith@atrad.adelaide.edu.au, gibbs@freefall.freebsd.org, phk@critter.tfs.com, jkh@time.cdrom.com, obrien@cs.ucdavis.edu, freebsd-hackers@FreeBSD.org In-Reply-To: <199601131402.AAA19555@genesis.atrad.adelaide.edu.au> from "Michael Smith" at Jan 14, 96 00:32:07 am X-Mailer: ELM [version 2.4 PL24] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-hackers@FreeBSD.org Precedence: bulk > > The private address space has the advantage of isolating potentially > > nasty ("scribble on the kernel") drivers, and the disadvantage of > > additional protection domain crossing (ala NetWare 4.x "memory > > protection"). > > With all the hoohah on pipelining and speculative execution and all that > crap, one never reads much about improvements in these issues (nor TLA and > friends). Is this domain crossing still expensive on newer processors? > (In context, I guess newer means P5+) Doing protection domain crossing is more expensive than not doing it. There *is* a method which uses the anonymity of pages in a "very large address space" (say 64 bits), where it "just works" if you get the right page and faults if you don't. The magic is that with a very large space, you can "hide" pages with a high statistical probability that it will be impossible to locate a particular page without faulting instead, since there are many many orders of magnitudes more unmapped pages than mapped ones. I haven't seen this tried on anything less than a 64 bit processor. Terry Lambert terry@lambert.org --- Any opinions in this posting are my own and not those of my present or previous employers.