Avi Kivity wrote Thu, 13 Nov 2008 14:33:16 +0200: > Michael Tokarev wrote: >> Somewhere between kvm-75 and kvm-78, the >> mentioned commands has been slowed down >> to insane levels. By "insane" I mean to >> take about 10 minutes(!) to save/load a >> 128MB RAM/1GB HDD VM's state. It used >> to require several seconds for much larger >> VMs... >> >> Here's a typical sequence of system calls >> during savevm: > [snip strace] > >> As you see, it writes 2 bytes, llseeks to THE SAME >> position, writes next 2 bytes and so on. This takes >> HUGE amount of time, and can be done, in most cases, >> in a single write without any seeks. >> >> Is it just me or are savevm/loadvm/delvm really THAT >> broken? > > It's qcow2 that is broken, with the new default cache=writethrough. > Does cache=writeback speed things up?
Please excuse me for this long delay replying... I tried other solutions meanwhile (migrate to exec:), but did not succeed there either. Well. While with writeback mode, the speed is definitely better. But it is still very very slow - not THAT terrible, but it still takes several mins to complete a 512MB VM with a single 4Gb qcow2 file. > This is probably block reference counts being updated. There were some > batching patches posted, but they have not been applied yet, and are > probably insufficient for savevm. Oh well.... :( So it really is that there's no way to "freeze" a vm currently. savevm/loadvm is too slow to be useful, and migrate does not work with local files (yet)... >> And since migration to disk has been removed too, >> there's no way currently to save the VM state... > > That's being restored. Thanks! Tried that (current patches), does not quite here yet :) /mjt -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
