From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jacob Gorm Hansen Subject: Re: Idea: Small Address Spaces Date: Tue, 05 Apr 2005 20:52:22 -0700 Message-ID: <42535CF6.3040102@diku.dk> References: <4251D3DC.8040309@diku.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4251D3DC.8040309@diku.dk> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org Jacob Gorm Hansen wrote: > hi, > > in the cases where users (like me) wish to run Xen with MPI on Ethernets > or similar, and don't care too much about driver isolation, I am > thinking of trying to apply Jochen Liedtke's old 'small address spaces' > hack, to see if I can improve domU I/O performance. > > My idea is to reserve some additional virtual address space below Xen, > e.g. at 0xF0000000, and map the kernel part of dom0* there permanently. > The user space part of dom0 I would map as normal from 0 - 0xC0000000, > to avoid relinking dom0 applications. I would use the segments to keep > the domUs below 0xF0000000. In this way, TLB flushes should only be > necessary when dom0 exits to user space, not when handling interrupts or > when domUs are asking for I/O. Hmmm turns out this is pretty hard to do without relinking userspace, as naturally the linux0 likes to peek and poke user-space addresses itself, as does Xen. I guess what I could do (my original plan actually, before I got too clever for my own good), would be to squeeze userspace into the permanent mapping as well, and then have a relinked busybox or similar in there, instead of a full, standard Linux disto. Jacob