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Joao Martins
15c3ef8b5e
Recent x86/time changes improved a lot of the monotonicity in xen
timekeeping, making it much harder to observe time going backwards.
Although platform timer can't be expected to be perfectly in sync with
TSC and so get_s_time won't be guaranteed to always return
monotonically increasing values across cpus. This is the case in some
of the boxes I am testing with, observing sometimes ~100 warps (of
very few nanoseconds each) after a few hours.
This patch introduces support for using TSC as platform time source
which is the highest resolution time and most performant to get.
Though there are also several problems associated with its usage, and
there isn't a complete (and architecturally defined) guarantee that
all machines will provide reliable and monotonic TSC in all cases (I
believe Intel to be the only that can guarantee that?). For this reason
it's not used unless administrator changes "clocksource" boot option
to "tsc". Initializing TSC clocksource requires all CPUs up to have
the tsc reliability checks performed. init_xen_time is called before
all CPUs are up, so for example we would start with HPET (or ACPI,
PIT) at boot time, and switch later to TSC. The switch then happens on
verify_tsc_reliability initcall that is invoked when all CPUs are up.
When attempting to initialize TSC we also check for time warps and if
it has invariant TSC. Note that while we deem reliable a CONSTANT_TSC
with no deep C-states, it might not always be the case, so we're
conservative and allow TSC to be used as platform timer only with
invariant TSC. Additionally we check if CPU Hotplug isn't meant to be
performed on the host which will either be when max vcpus and
num_present_cpu are the same. This is because a newly hotplugged CPU
may not satisfy the condition of having all TSCs synchronized - so
when having tsc clocksource being used we allow offlining CPUs but not
onlining any ones back. Finally we prevent TSC from being used as
clocksource on multiple sockets because it isn't guaranteed to be
invariant. Further relaxing of this last requirement is added in a
separate patch, such that we allow vendors with such guarantee to use
TSC as clocksource. In case any of these conditions is not met, we
keep the clocksource that was previously initialized on init_xen_time.
Since b64438c7c ("x86/time: use correct (local) time stamp in
constant-TSC calibration fast path") updates to cpu time use local
stamps, which means platform timer is only used to seed the initial
cpu time. We further introduce a new rendezvous function
(nop_rendezvous) which doesn't require synchronization between master
and slave CPUS and just reads calibration_rendezvous struct and writes
it down the stime and stamp to the cpu_calibration struct to be used
later on. With clocksource=tsc there is no need to be in sync with
another clocksource, so we reseed the local/master stamps to be values
of TSC and update the platform time stamps accordingly. Time
calibration is set to 1sec after we switch to TSC, thus these stamps
are reseeded to also ensure monotonic returning values right after the
point we switch to TSC. This is to remove the possibility of having
inconsistent readings in this short period (i.e. until calibration
fires).
Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
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http://www.xen.org/
What is Xen?
============
Xen is a Virtual Machine Monitor (VMM) originally developed by the
Systems Research Group of the University of Cambridge Computer
Laboratory, as part of the UK-EPSRC funded XenoServers project. Xen
is freely-distributable Open Source software, released under the GNU
GPL. Since its initial public release, Xen has grown a large
development community, spearheaded by xen.org (http://www.xen.org).
This file contains some quick-start instructions to install Xen on
your system. For more information see http:/www.xen.org/ and
http://wiki.xen.org/
Quick-Start Guide
=================
First, this is just a quick-start guide. For more comprehensive
information see the INSTALL file and the Xen wiki at
http://wiki.xenproject.org and in particular
http://wiki.xenproject.org/wiki/Getting_Started.
Second, there are a number of prerequisites for building a Xen source
release. Make sure you have all the following installed, either by
visiting the project webpage or installing a pre-built package
provided by your OS distributor:
* GNU Make v3.80 or later
* C compiler and linker:
- For x86:
- GCC 4.1.2_20070115 or later
- GNU Binutils 2.16.91.0.5 or later
or
- Clang/LLVM 3.5 or later
- For ARM:
- GCC 4.8 or later
- GNU Binutils 2.24 or later
* Development install of zlib (e.g., zlib-dev)
* Development install of Python v2.3 or later (e.g., python-dev)
* Development install of curses (e.g., libncurses-dev)
* Development install of openssl (e.g., openssl-dev)
* Development install of x11 (e.g. xorg-x11-dev)
* Development install of uuid (e.g. uuid-dev)
* Development install of yajl (e.g. libyajl-dev)
* Development install of libaio (e.g. libaio-dev) version 0.3.107 or
greater.
* Development install of GLib v2.0 (e.g. libglib2.0-dev)
* Development install of Pixman (e.g. libpixman-1-dev)
* pkg-config
* bridge-utils package (/sbin/brctl)
* iproute package (/sbin/ip)
* GNU bison and GNU flex
* GNU gettext
* ACPI ASL compiler (iasl)
* Libc multiarch package (e.g. libc6-dev-i386 / glibc-devel.i686).
Required when building on a 64-bit platform to build
32-bit components which are enabled on a default build.
In addition to the above there are a number of optional build
prerequisites. Omitting these will cause the related features to be
disabled at compile time:
* Development install of Ocaml (e.g. ocaml-nox and
ocaml-findlib). Required to build ocaml components which
includes the alternative ocaml xenstored.
* cmake (if building vtpm stub domains)
* markdown
* figlet (for generating the traditional Xen start of day banner)
* systemd daemon development files
* Development install of libnl3 (e.g., libnl-3-200,
libnl-3-dev, etc). Required if network buffering is desired
when using Remus with libxl. See docs/README.remus for detailed
information.
* 16-bit x86 assembler, loader and compiler for qemu-traditional / rombios
(dev86 rpm or bin86 & bcc debs)
Second, you need to acquire a suitable kernel for use in domain 0. If
possible you should use a kernel provided by your OS distributor. If
no suitable kernel is available from your OS distributor then refer to
http://wiki.xen.org/wiki/XenDom0Kernels for suggestions for
suitable kernels to use.
If you are looking to compile a Dom0 kernel from source, please refer to
http://wiki.xen.org/wiki/XenParavirtOps.
[NB. Unless noted otherwise, all the following steps should be
performed with root privileges.]
1. Download and untar the source tarball file. This will be a
file named xen-unstable-src.tgz, or xen-$version-src.tgz.
You can also pull the current version from the git or mercurial
repositories at http://xenbits.xen.org/
# tar xzf xen-unstable-src.tgz
Assuming you are using the unstable tree, this will
untar into xen-unstable. The rest of the instructions
use the unstable tree as an example, substitute the
version for unstable.
2. cd to xen-unstable (or whatever you sensibly rename it to).
3. For the very first build, or if you want to destroy build trees,
perform the following steps:
# ./configure
# make world
# make install
See the documentation in the INSTALL file for more info.
This will create and install onto the local machine. It will build
the xen binary (xen.gz), the tools and the documentation.
You can override the destination for make install by setting DESTDIR
to some value.
4. To rebuild an existing tree without modifying the config:
# make dist
This will build and install xen, tools, and docs into the local dist/
directory.
You can override the destination for make install by setting DISTDIR
to some value.
make install and make dist differ in that make install does the
right things for your local machine (installing the appropriate
version of udev scripts, for example), but make dist includes all
versions of those scripts, so that you can copy the dist directory
to another machine and install from that distribution.
xenstore: xenstored and oxenstored
====================================
Xen uses a configuration database called xenstore [0] to maintain configuration
and status information shared between domains. A daemon is implemented as part
of xenstore to act as an interface for access to the database for dom0 and
guests. Two xenstored daemons are supported, one written in C which we refer
to as the xenstored (sometimes referred to as cxenstored), and another written
in Ocaml called oxenstored. Details for xenstore and the different
implementations can be found on the wiki's xenstore reference guide [1] and
the xenstored [2] page. You can choose which xenstore you want to enable as
default on a system through configure:
./configure --with-xenstored=xenstored
./configure --with-xenstored=oxenstored
By default oxenstored will be used if the ocaml development tools are found.
If you enable oxenstored the xenstored will still be built and installed,
the xenstored used can be changed through the configuration file:
/etc/sysconfig/xencommons
or
/etc/default/xencommons
You can change the preferred xenstored you want to use in the configuration
but since we cannot stop the daemon a reboot will be required to make the
change take effect.
[0] http://wiki.xen.org/wiki/XenStore
[1] http://wiki.xen.org/wiki/XenStoreReference
[2] http://wiki.xen.org/wiki/Xenstored
Python Runtime Libraries
========================
Various tools, such as pygrub, have the following runtime dependencies:
* Python 2.3 or later.
URL: http://www.python.org/
Debian: python
Intel(R) Trusted Execution Technology Support
=============================================
Intel's technology for safer computing, Intel(R) Trusted Execution Technology
(Intel(R) TXT), defines platform-level enhancements that provide the building
blocks for creating trusted platforms. For more information, see
http://www.intel.com/technology/security/.
Intel(R) TXT support is provided by the Trusted Boot (tboot) module in
conjunction with minimal logic in the Xen hypervisor.
Tboot is an open source, pre- kernel/VMM module that uses Intel(R) TXT to
perform a measured and verified launch of an OS kernel/VMM.
The Trusted Boot module is available from
http://sourceforge.net/projects/tboot. This project hosts the code in a
mercurial repo at http://tboot.sourceforge.net/hg/tboot.hg and contains
tarballs of the source. Instructions in the tboot README describe how
to modify grub.conf to use tboot to launch Xen.
There are optional targets as part of Xen's top-level makefile that will
download and build tboot: install-tboot, build-tboot, dist-tboot, clean-tboot.
These will download the latest tar file from the SourceForge site using wget,
then build/install/dist according to Xen's settings.