On Thu, May 14, 2020 at 05:51:02PM +0200, Paolo Bonzini wrote: > On 14/05/20 17:34, Daniel P. Berrangé wrote: > > Yeah, the key thing is that you really want to be able to provide the > > whole initial config in one go as an atomic action. I don't want to > > issue 100 individual QMP commands to load each initial device. > > Why? I think if we do something like the qemu-vm-$TARGET that you > propose below, there's absolutely no difference between the two.
Ok, I should clarify. I don't want to do 100 individual serialized round-trip request+reply, as that'd create latency on startup. 100 pipelined/parallelized request+reply would be ok, as you'll not have the synchronization delay for each command. Today the biggest cause of slow startup in libvirt, is issuing something like 100+ serialized QMP calls to check status of individual CPUID features. Possibly this is already just a libvirt bug we can could just stuff all 100 qom-get queries down the pipe in one go and have 1 wait for replies to arrive. > Then you'd have a > > qemu-run /some/file.yaml > > (notice the lack of $TARGET) that takes care of starting the VM. > > > I tend to think we'd be better served by focusing on introducing a new set > > of binaries, qemu-vm-$TARGET, which exclusively use a new config syntax, > > free of any legacy baggage present in qemu-system-$TARGET. > > > > Work on qemu-vm-$TARGET will involve refactoring, and that will certainly > > risk causing bugs in qemu-system-$TARGET. The premise though is that this > > risk is lower, than if we tried to retrofit a new config syuntax directly > > into qemu-system-$TARGET. > > > > In particular I think it is basically impossible to do any meaningful > > changes in the main() method of softmmu/vl.c, due to the fragile ordering > > for creation of various different devices/backends, and its interaction > > with the argv parsing. By using a new qemu-vm-$TARGET we can have a new > > softmmu/vm.c, instead of vl.c. We'll still likely need to modify parts of > > vl.c to use new/changed API calls, but that's less distruptive, as we > > can leave the crazy logic for ordering of device creation untouched. > > Agreed. > > Paolo > Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|