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tests/qtest: massively speed up migration-test
Daniel P. Berrangé authored 
The migration test cases that actually exercise live migration want to
ensure there is a minimum of two iterations of pre-copy, in order to
exercise the dirty tracking code.

Historically we've queried the migration status, looking for the
'dirty-sync-count' value to increment to track iterations. This was
not entirely reliable because often all the data would get transferred
quickly enough that the migration would finish before we wanted it
to. So we massively dropped the bandwidth and max downtime to
guarantee non-convergance. This had the unfortunate side effect
that every migration took at least 30 seconds to run (100 MB of
dirty pages / 3 MB/sec).

This optimization takes a different approach to ensuring that a
mimimum of two iterations. Rather than waiting for dirty-sync-count
to increment, directly look for an indication that the source VM
has dirtied RAM that has already been transferred.

On the source VM a magic marker is written just after the 3 MB
offset. The destination VM is now montiored to detect when the
magic marker is transferred. This gives a guarantee that the
first 3 MB of memory have been transferred. Now the source VM
memory is monitored at exactly the 3MB offset until we observe
a flip in its value. This gives us a guaranteed that the guest
workload has dirtied a byte that has already been transferred.

Since we're looking at a place that is only 3 MB from the start
of memory, with the 3 MB/sec bandwidth, this test should complete
in 1 second, instead of 30 seconds.

Once we've proved there is some dirty memory, migration can be
set back to full speed for the remainder of the 1st iteration,
and the entire of the second iteration at which point migration
should be complete.

On a test machine this further reduces the migration test time
from 8 minutes to 1 minute 40.

Signed-off-by: default avatarDaniel P. Berrangé <berrange@redhat.com>
Message-Id: <20230601161347.1803440-11-berrange@redhat.com>
Signed-off-by: default avatarThomas Huth <thuth@redhat.com>
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.github/workflows
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accel
audio
authz
backends
block
bsd-user
chardev
common-user
configs
contrib
crypto
disas
docs
dump
ebpf
fpu
fsdev
gdb-xml
gdbstub
host/include
hw
include
io
libdecnumber
linux-headers
linux-user
migration
monitor
nbd
net
pc-bios
plugins
po
python
qapi
qga
qobject
qom
replay
roms
scripts
scsi
semihosting
softmmu
stats
storage-daemon
stubs
subprojects
target
tcg
tests
tools
trace
ui
util
.dir-locals.el
.editorconfig
.exrc
.gdbinit
.git-blame-ignore-revs
.gitattributes
.gitignore
.gitlab-ci.yml
.gitmodules
.gitpublish
.mailmap
.patchew.yml
.readthedocs.yml
.travis.yml
COPYING
COPYING.LIB
Kconfig
Kconfig.host
LICENSE
MAINTAINERS
Makefile
README.rst
VERSION
block.c
blockdev-nbd.c
blockdev.c
blockjob.c
configure
cpu.c
cpus-common.c
event-loop-base.c
gitdm.config
hmp-commands-info.hx
hmp-commands.hx
iothread.c
job-qmp.c
job.c
memory_ldst.c.inc
meson.build
meson_options.txt
module-common.c
os-posix.c
os-win32.c
page-vary-common.c
page-vary.c
qemu-bridge-helper.c
qemu-edid.c
qemu-img-cmds.hx
qemu-img.c
qemu-io-cmds.c
qemu-io.c
qemu-keymap.c
qemu-nbd.c
qemu-options.hx
qemu.nsi
qemu.sasl
replication.c
trace-events
version.rc
README.rst

QEMU README

QEMU is a generic and open source machine & userspace emulator and virtualizer.

QEMU is capable of emulating a complete machine in software without any need for hardware virtualization support. By using dynamic translation, it achieves very good performance. QEMU can also integrate with the Xen and KVM hypervisors to provide emulated hardware while allowing the hypervisor to manage the CPU. With hypervisor support, QEMU can achieve near native performance for CPUs. When QEMU emulates CPUs directly it is capable of running operating systems made for one machine (e.g. an ARMv7 board) on a different machine (e.g. an x86_64 PC board).

QEMU is also capable of providing userspace API virtualization for Linux and BSD kernel interfaces. This allows binaries compiled against one architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a different architecture ABI (e.g. the Linux x86_64 ABI). This does not involve any hardware emulation, simply CPU and syscall emulation.

QEMU aims to fit into a variety of use cases. It can be invoked directly by users wishing to have full control over its behaviour and settings. It also aims to facilitate integration into higher level management layers, by providing a stable command line interface and monitor API. It is commonly invoked indirectly via the libvirt library when using open source applications such as oVirt, OpenStack and virt-manager.

QEMU as a whole is released under the GNU General Public License, version 2. For full licensing details, consult the LICENSE file.

Documentation

Documentation can be found hosted online at https://www.qemu.org/documentation/. The documentation for the current development version that is available at https://www.qemu.org/docs/master/ is generated from the docs/ folder in the source tree, and is built by Sphinx.

Building

QEMU is multi-platform software intended to be buildable on all modern Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety of other UNIX targets. The simple steps to build QEMU are:

mkdir build
cd build
../configure
make

Additional information can also be found online via the QEMU website:

Submitting patches

The QEMU source code is maintained under the GIT version control system.

git clone https://gitlab.com/qemu-project/qemu.git

When submitting patches, one common approach is to use 'git format-patch' and/or 'git send-email' to format & send the mail to the qemu-devel@nongnu.org mailing list. All patches submitted must contain a 'Signed-off-by' line from the author. Patches should follow the guidelines set out in the style section of the Developers Guide.

Additional information on submitting patches can be found online via the QEMU website

The QEMU website is also maintained under source control.

git clone https://gitlab.com/qemu-project/qemu-web.git

A 'git-publish' utility was created to make above process less cumbersome, and is highly recommended for making regular contributions, or even just for sending consecutive patch series revisions. It also requires a working 'git send-email' setup, and by default doesn't automate everything, so you may want to go through the above steps manually for once.

For installation instructions, please go to

The workflow with 'git-publish' is:

$ git checkout master -b my-feature
$ # work on new commits, add your 'Signed-off-by' lines to each
$ git publish

Your patch series will be sent and tagged as my-feature-v1 if you need to refer back to it in the future.

Sending v2:

$ git checkout my-feature # same topic branch
$ # making changes to the commits (using 'git rebase', for example)
$ git publish

Your patch series will be sent with 'v2' tag in the subject and the git tip will be tagged as my-feature-v2.

Bug reporting

The QEMU project uses GitLab issues to track bugs. Bugs found when running code built from QEMU git or upstream released sources should be reported via:

If using QEMU via an operating system vendor pre-built binary package, it is preferable to report bugs to the vendor's own bug tracker first. If the bug is also known to affect latest upstream code, it can also be reported via GitLab.

For additional information on bug reporting consult:

ChangeLog

For version history and release notes, please visit https://wiki.qemu.org/ChangeLog/ or look at the git history for more detailed information.

Contact

The QEMU community can be contacted in a number of ways, with the two main methods being email and IRC

Information on additional methods of contacting the community can be found online via the QEMU website: