Eduardo Habkost <[email protected]> writes: > My apologies, this was lost under the noise in my mail inbox. > (I promise I'm trying to improve) > > On Wed, Mar 31, 2021 at 01:39:48PM +0200, Vitaly Kuznetsov wrote: >> Commit 561dbb41b1d7 "i386: Make migration fail when Hyper-V reenlightenment >> was enabled but 'user_tsc_khz' is unset" forbade migrations with when guest >> has opted for reenlightenment notifications but 'tsc-frequency' wasn't set >> explicitly on the command line. This works but the migration fails late and >> this may come as an unpleasant surprise. To make things more explicit, >> require 'tsc-frequency=' on the command line when 'hv-reenlightenment' was >> enabled. Make the change affect 6.0+ machine types only to preserve >> previously-valid configurations. >> >> Signed-off-by: Vitaly Kuznetsov <[email protected]> >> Acked-by: Dr. David Alan Gilbert <[email protected]> > > Even if the 6.0 release gets delayed, I wouldn't be comfortable > including this in a -rc4. > > What if the user does not plan to live migrate the machine at > all? Why is this case different from the ~25 > migrate_add_blocker() calls in QEMU, where we block migration but > still let the VM run?
The question is when do we want to let the user know about the problem. By refusing to start with 'hv-reenlightenment' and without 'tsc-frequency' we make it sure he knows early. We can, indeed, replace this with migrate_add_blocker() call but the fact that the VM is not migratable may come as a (late) surprise (we can certainly print a warning but these may be hidden by upper layers). Also, v1 of this patch was implementing a slightly different approach failing the migration late if we can't set tsc frequency on the destination host. Explicit 'tsc-frequency=' was not required. Personally, I'm comfortable with any approach, please advise. -- Vitaly
