Re: [Qemu-devel] [PATCH v4 00/20] monitor: add asynchronous command type

[Gerd Hoffmann]

  Hi,

> > This is not meant for some long-running job which you have to manage.
> >
> > Allowing commands being asynchronous makes sense for things which (a)
> > typically don't take long, and (b) don't need any management.
> >
> > So, if the connection goes down the job is simply canceled, and after
> > reconnecting the management can simply send the same command again.
> 
> Is this worth its own infrastructure?
> 
> Would you hazard a guess on how many commands can take long enough to
> demand a conversion to asynchronous, yet not need any management?

Required:
  screendump with qxl (needs round-drop to spice-server display thread
  for fully up-to-date screen content, due to lazy rendering).

Nice to have:
  Move anything which needs more than a milisecond to a thread or
  coroutine, so we avoid monitor commands causing guest-visible latency
  spikes due to holding the big qemu lock for too long.

  From a quick scan through monitor help hot candidates are screendump
  and pmemsave because they might write rather large data files.

  Dunno about savevm/loadvm.  I think they stop the guest anyway.  So
  moving them to async probably doesn't buy us much, at least from a
  latency point of view.

cheers,
  Gerd