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Add PRE_COPY support for live migration. This functionality may reduce the downtime upon STOP_COPY as of letting the target machine to get some 'initial data' from the source once the machine is still in its RUNNING state and let it prepares itself pre-ahead to get the final STOP_COPY data. As the Virtio specification does not support reading partial or incremental device contexts. This means that during the PRE_COPY state, the vfio-virtio driver reads the full device state. As the device state can be changed and the benefit is highest when the pre copy data closely matches the final data we read it in a rate limiter mode. This means we avoid reading new data from the device for a specified time interval after the last read. With PRE_COPY enabled, we observed a downtime reduction of approximately 70-75% in various scenarios compared to when PRE_COPY was disabled, while keeping the total migration time nearly the same. Signed-off-by: Yishai Hadas <yishaih@nvidia.com> Link: https://lore.kernel.org/r/20241113115200.209269-7-yishaih@nvidia.com Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.