Re: [libvirt RFC] add API for parallel Saves (not for committing)
On Thu, Apr 21, 2022 at 18:08:36 +0100, Daniel P. Berrangé wrote:
On Thu, Apr 14, 2022 at 09:54:16AM +0200, Claudio Fontana wrote:
> RFC, starting point for discussion.
>
> Sketch API changes to allow parallel Saves, and open up
> and implementation for QEMU to leverage multifd migration to files,
> with optional multifd compression.
>
> This allows to improve save times for huge VMs.
>
> The idea is to issue commands like:
>
> virsh save domain /path/savevm --parallel --parallel-connections 2
>
> and have libvirt start a multifd migration to:
>
> /path/savevm : main migration connection
> /path/savevm.1 : multifd channel 1
> /path/savevm.2 : multifd channel 2
At a conceptual level the idea would to still have a single file,
but have threads writing to different regions of it. I don't think
Note that guys from Virtuozzo planned to do enhancements to the
migration code which would allow post-copy style migration into a file.
For this they need a memory image with "random access" especially for
the loading part. Now the idea was to use a different image format,
something more like a qcow2 container (or actually a qcow2 image) to
store the memory pages but allow random access.
Now with that a parallel output could also theoretically be possible
IIRC.
Unfortunately I have no idea how their work is progressing, it was a
while ago already we've discussed it here.