From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S272901AbTG3OFb (ORCPT ); Wed, 30 Jul 2003 10:05:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S272902AbTG3OFa (ORCPT ); Wed, 30 Jul 2003 10:05:30 -0400 Received: from mail.jlokier.co.uk ([81.29.64.88]:56963 "EHLO mail.jlokier.co.uk") by vger.kernel.org with ESMTP id S272901AbTG3OFY (ORCPT ); Wed, 30 Jul 2003 10:05:24 -0400 Date: Wed, 30 Jul 2003 15:05:22 +0100 From: Jamie Lokier To: Helge Hafting Cc: linux-kernel@vger.kernel.org Subject: Re: The well-factored 386 Message-ID: <20030730140522.GA21665@mail.jlokier.co.uk> References: <03072809023201.00228@linux24> <20030728093245.60e46186.davem@redhat.com> <20030728194127.GA10673@mail.jlokier.co.uk> <20030729111423.GA5320@hh.idb.hist.no> <20030729161951.GA15889@mail.jlokier.co.uk> <20030730071131.GA6282@hh.idb.hist.no> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20030730071131.GA6282@hh.idb.hist.no> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Helge Hafting wrote: > So you can probably use paging in "forreal" mode too. I believe > you only get the page table's memory mapping capabilities > though, I don't think you get protection of "kernel" pages > without protection enabled. > > You could still "hide" kernel memory by giving userspace another > page table, but that means page table switching on each > syscall which kills performance worse than interrupt handling > in protecxted mode. Yes, that's exactly what I had in mind. You say that page table switching kills performance, but consider Ingo's latest 64G patches do exactly that, and performance, though degraded, is not too bad. Whether it's worth doing that would depend on the balance of interrupts vs. syscalls. Some embedded applications are dominated by interrupts, and there are apps which avoid syscalls altogether during the main part of their running. -- Jamie