Add more configurable settings for VMs #167
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virshhas a few tunables that can be turned into additional metainformation about the VM. Some choice examples include:migrate --auto-converge: Adjust autoconverge settings during the migration, might be useful to investigate in detail and tune.migrate --compressed: Adjust compression settings during migration, might be useful to investigate in detail and tune.migrate-[get|set]maxdowntime: Adjust the maximum amount of downtime (in ms) for the final pause of the VM during a migration. Default is 300ms.migrate-[get|set]speed: Adust the maximum speed of the migration copies. The default and the units specified don't make a whole lot of sense (it says the unit isMiBbut the value is8796093022207or about 8 EiB which can't be right).migrate-compcache: Adjust the compression cache size. Default is 64 MiB.schedinfo: Shows or tunes scheduler info. Could be useful to tune.Some things I noticed during this infodump that might also be useful:
blkdeviotune: Tune block I/O settings (limit IOPS, etc.). Needs more reading.numatune: Tune NUMA settings. Needs more reading.ttyconsole: Shows the raw/dev/ttydevice for the domain console. Could help with remote console support perhaps?domblkstat: Shows block device stats for the VM. Could provide more info.dommemstat: Shows memory stats for the VM. Could provide more info.domstats: Show all stats ("balloon" = "mem") for the VM. Could provide mode info. Do I use this already?domjobinfo: Show information on migration jobs. Might be very useful to observe with the migrate command to provide progress updates during live migrations. "--completed" shows finished job stats for the final update.domdisplay: Show the URI of the VNC/Spice/RDP console of the VM.domfsinfo: Shows the (real) mapping of volumes in the guest. Could be very useful in VM information showing.reset: Torebootwhatdestroyis toshutdown. Might be worth implementing ifrebootcommands time out.screenshot: Takes a screenshot of the console. Might be worth implementing.send-key: Sends a keypress to the domain. Might be worth implementing.Included in 1.0 milestone as some of these have good potential but more R&D is required.
migrate-setmaxdowntimehas become a priority as I've seen more and more VMs in the wild where this has to be tuned.This also makes me think of doing some enhancements around VM migrations to better capture what's going on with them. While the current process works, it can also be error prone and leave VMs in weird states if it fails. The opportunity to use
domjobinfoto get live stats about the migration is also compelling, as would a command to view these stats during the migration.Decoupling the last two update items, I think implementing
maxdowntimeas a new meta field and then simply calling the relevant command on VM start/receive is best, as that can be done fairly easily. Enhancing VM migrations is a much bigger job, including ideally a move of those into the workers, so that can wait as a separate task.