annotate README @ 1557:e848e1d5ecd8

bitkeeper revision 1.1010 (40da8d0bAUpsJUh6bwWRl65Frtj_lQ)

README update
author kaf24@scramble.cl.cam.ac.uk
date Thu Jun 24 08:12:59 2004 +0000 (2004-06-24)
parents dee503a6c122
children 6802d4f0ce7f
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iap10@706 9
iap10@706 10 University of Cambridge Computer Laboratory
iap10@1476 11 15 Jun 2004
iap10@706 12
iap10@706 13 http://www.cl.cam.ac.uk/netos/xen
iap10@706 14
iap10@706 15 About the Xen Virtual Machine Monitor
iap10@706 16 =====================================
iap10@706 17
iap10@1061 18 "Xen" is a Virtual Machine Monitor (VMM) originally developed by the
iap10@1061 19 Systems Research Group of the University of Cambridge Computer
iap10@1061 20 Laboratory, as part of the UK-EPSRC funded XenoServers project.
iap10@706 21
iap10@706 22 The XenoServers project aims to provide a "public infrastructure for
iap10@706 23 global distributed computing", and Xen plays a key part in that,
iap10@706 24 allowing us to efficiently partition a single machine to enable
iap10@706 25 multiple independent clients to run their operating systems and
iap10@706 26 applications in an environment providing protection, resource
iap10@706 27 isolation and accounting. The project web page contains further
iap10@706 28 information along with pointers to papers and technical reports:
iap10@706 29 http://www.cl.cam.ac.uk/xeno
iap10@706 30
iap10@706 31 Xen has since grown into a project in its own right, enabling us to
iap10@706 32 investigate interesting research issues regarding the best techniques
iap10@706 33 for virtualizing resources such as the CPU, memory, disk and network.
iap10@706 34 The project has been bolstered by support from Intel Research
iap10@1476 35 Cambridge, and HP Labs, who are now working closely with us. We're
iap10@1476 36 also in receipt of support from Microsoft Research Cambridge to port
iap10@1476 37 Windows XP to run on Xen.
iap10@706 38
iap10@744 39 Xen enables multiple operating system images to execute concurrently
iap10@706 40 on the same hardware with very low performance overhead --- much lower
iap10@744 41 than commercial offerings for the same x86 platform.
iap10@706 42
iap10@706 43 This is achieved by requiring OSs to be specifically ported to run on
iap10@706 44 Xen, rather than allowing unmodified OS images to be used. Crucially,
iap10@706 45 only the OS needs to be changed -- all of the user-level application
iap10@744 46 binaries, libraries etc can run unmodified. Hence the modified OS
iap10@706 47 kernel can typically just be dropped into any existing OS distribution
iap10@706 48 or installation.
iap10@706 49
iap10@706 50 Xen currently runs on the x86 architecture, but could in principle be
iap10@744 51 ported to others. In fact, it would have been rather easier to write
iap10@744 52 Xen for pretty much any other architecture as x86 is particularly
iap10@744 53 tricky to handle. A good description of Xen's design, implementation
iap10@744 54 and performance is contained in our October 2003 SOSP paper, available
iap10@744 55 at http://www.cl.cam.ac.uk/netos/papers/2003-xensosp.pdf
iap10@706 56
iap10@1476 57 We have worked on porting 4 different operating systems to run
iap10@1476 58 on Xen: Linux 2.4/2.6, Windows XP, NetBSD and FreeBSD.
iap10@706 59
iap10@1476 60 The Linux 2.4 port (currently Linux 2.4.26) works very well -- we
iap10@706 61 regularly use it to host complex applications such as PostgreSQL,
iap10@744 62 Apache, BK servers etc. It runs every user-space applications we've
iap10@736 63 tried. We refer to our version of Linux ported to run on Xen as
iap10@1476 64 "XenLinux", although really it's just standard Linux ported to a new
kaf24@1213 65 virtual CPU architecture that we call xen-x86.
iap10@706 66
iap10@1061 67 NetBSD has been ported to Xen by Christian Limpach, and will hopefully
iap10@1061 68 soon become part of the standard release. Work on a FreeBSD port has
iap10@1061 69 been started by Kip Macy, and we hope to see this complete for the 1.3
iap10@1061 70 release.
iap10@706 71
iap10@706 72 The Windows XP port is nearly finished. It's running user space
iap10@706 73 applications and is generally in pretty good shape thanks to some hard
iap10@706 74 work by the team over the summer. Of course, there are issues with
iap10@706 75 releasing this code to others. We should be able to release the
iap10@736 76 source and binaries to anyone that has signed the Microsoft academic
iap10@736 77 source license, which these days has very reasonable terms. We are in
iap10@736 78 discussions with Microsoft about the possibility of being able to make
iap10@736 79 binary releases to a larger user community. Obviously, there are
iap10@744 80 issues with product activation in this environment which need to be
iap10@744 81 thought through.
iap10@706 82
iap10@1476 83 So, for the moment, you only get to run Linux 2.4/2.6 and NetBSD on
iap10@706 84 Xen, but we hope this will change before too long. Even running
iap10@706 85 multiple copies of the same OS can be very useful, as it provides a
iap10@706 86 means of containing faults to one OS image, and also for providing
iap10@706 87 performance isolation between the various OS, enabling you to either
iap10@706 88 restrict, or reserve resources for, particular VM instances.
iap10@706 89
iap10@744 90 It's also useful for development -- each version of Linux can have
iap10@706 91 different patches applied, enabling different kernels to be tried
iap10@706 92 out. For example, the "vservers" patch used by PlanetLab applies
iap10@706 93 cleanly to our ported version of Linux.
iap10@706 94
iap10@706 95 We've successfully booted over 128 copies of Linux on the same machine
iap10@706 96 (a dual CPU hyperthreaded Xeon box) but we imagine that it would be
iap10@706 97 more normal to use some smaller number, perhaps 10-20.
iap10@706 98
iap10@706 99
iap10@706 100 Hardware support
iap10@706 101 ================
iap10@706 102
iap10@706 103 Xen is intended to be run on server-class machines, and the current
iap10@706 104 list of supported hardware very much reflects this, avoiding the need
kaf24@751 105 for us to write drivers for "legacy" hardware. It is likely that some
kaf24@751 106 desktop chipsets will fail to work properly with the default Xen
kaf24@751 107 configuration: specifying 'noacpi' or 'ignorebiostables' when booting
kaf24@751 108 Xen may help in these cases.
iap10@706 109
iap10@706 110 Xen requires a "P6" or newer processor (e.g. Pentium Pro, Celeron,
iap10@706 111 Pentium II, Pentium III, Pentium IV, Xeon, AMD Athlon, AMD Duron).
iap10@706 112 Multiprocessor machines are supported, and we also have basic support
iap10@744 113 for HyperThreading (SMT), although this remains a topic for ongoing
iap10@1476 114 research. We're also working on an AMD x86_64 port (though Xen should
iap10@744 115 run on Opterons in 32-bit mode just fine).
iap10@706 116
iap10@744 117 Xen can currently use up to 4GB of memory. It's possible for x86
iap10@706 118 machines to address more than that (64GB), but it requires using a
iap10@706 119 different page table format (3-level rather than 2-level) that we
iap10@706 120 currently don't support. Adding 3-level PAE support wouldn't be
iap10@706 121 difficult, but we'd also need to add support to all the guest
iap10@706 122 OSs. Volunteers welcome!
iap10@706 123
iap10@1476 124 In contrast to previous Xen versions, in Xen 2.0 device drivers run
iap10@1476 125 within a privileged guest OS rather than within Xen itself. This means
iap10@1476 126 that we should be compatible with the full set of device hardware
iap10@1476 127 supported by Linux. The default XenLinux build contains support for
iap10@1476 128 relatively modern server-class network and disk hardware, but you can
iap10@1476 129 add suppport for other hardware by configuring your XenLinux kernel in
iap10@1476 130 the normal way (e.g. "make xconfig").
iap10@706 131
iap10@706 132
iap10@1476 133 Building Xen and XenLinux
iap10@1476 134 =========================
iap10@744 135
iap10@1476 136 The public master BK repository for the 2.0 release lives at:
iap10@1476 137 bk://xen.bkbits.net/xeno-2.0.bk
iap10@747 138
iap10@771 139 To fetch a local copy, install the BitKeeper tools, then run:
iap10@1476 140 'bk clone bk://xen.bkbits.net/xeno-2.0.bk'
iap10@771 141
iap10@1476 142 You can do a complete build of Xen, the control tools, and the
iap10@1476 143 XenLinux kernel images with "make world". This can take 10 minutes
iap10@1476 144 even on a fast machine. If you're on an SMP machine you may wish to
kaf24@1557 145 give the '-j4' argument to make to get a parallel build. All of the
kaf24@1557 146 files that are built are placed under the ./install directory. You
kaf24@1557 147 can then install everything to the standard system directories
kaf24@1557 148 (e.g. /boot, /usr/bin, /usr/lib/python/ etc) by typing "make install".
iap10@771 149
kaf24@1557 150 Take a look in install/boot/:
kaf24@1557 151 install/boot/xen.gz The Xen 'kernel' (formerly image.gz)
kaf24@1557 152 install/boot/vmlinuz-2.4.26-xen0 Domain 0 XenLinux kernel (xenolinux.gz)
kaf24@1557 153 install/boot/vmlinuz-2.4.26-xenU Unprivileged XenLinux kernel
iap10@771 154
kaf24@1557 155 The difference between the two Linux kernels that are built is
kaf24@1557 156 due to the configuration file used for each. The "U" suffixed
kaf24@1557 157 unprivileged version doesn't contain any of the physical hardware
kaf24@1557 158 device drivers, so is 30% smaller and hence may be preferred for
kaf24@1557 159 your non-privileged domains.
kaf24@1557 160
kaf24@1557 161 The install/boot directory will also contain the config files
kaf24@1557 162 used for building the XenLinux kernels, and also versions of Xen
kaf24@1557 163 and XenLinux kernels that contain debug symbols (xen-syms and
kaf24@1557 164 vmlinux-syms-2.4.26-xen0) which are essential for interpreting crash
kaf24@1557 165 dumps.
kaf24@1557 166
kaf24@1557 167 Inspect the Makefile if you want to see what goes on during a
iap10@1476 168 build. Building Xen and the tools is straightforward, but XenLinux is
iap10@1476 169 more complicated. The makefile needs a 'pristine' linux kernel tree
iap10@1476 170 which it will then add the Xen architecture files to. You can tell the
iap10@1476 171 makefile the location of the appropriate linux compressed tar file by
iap10@1476 172 setting the LINUX_SRC environment variable
iap10@1476 173 (e.g. "LINUX_SRC=/tmp/linux-2.4.26.tar.gz make world") or by placing
iap10@1476 174 the tar file somewhere in the search path of LINUX_SRC_PATH which
iap10@1476 175 defaults to ".:..". If the makefile can't find a suitable kernel tar
iap10@1476 176 file it attempts to download it from kernel.org, but this won't work
iap10@1476 177 if you're behind a firewall.
iap10@1476 178
iap10@1476 179 After untaring the pristine kernel tree, the makefile uses the
iap10@1476 180 'mkbuildtree' script to add the Xen patches the kernel. "make world"
iap10@1476 181 then build two different XenLinux images, one with a "-xen0" extension
iap10@1476 182 which contains hardware device drivers and is intended to be used in
iap10@1476 183 the first virtual machine ("domain 0"), and one with a "-xenU"
iap10@1476 184 extension that just contains virtual-device drivers. The latter can be
iap10@1476 185 used for all non hardware privileged domains, and is substantially
iap10@1476 186 smaller than the other kernel with its selection of hardware drivers.
iap10@1476 187
iap10@1476 188 If you don't want to use bitkeeper to download the source, you can
iap10@1476 189 download prebuilt binaries and src tar balls from the project
iap10@1476 190 downloads page: http://www.cl.cam.ac.uk/netos/xen/downloads/