On Wed, Jan 04, 2017 at 09:37:39AM +0100, Gerd Hoffmann wrote: > Hi, > > > It is quite simple, there would be a 100% to a 1% menu item. It would look > > like > > this: > > > > Speed > > ------- > > 100% > > 90% > > 80% > > 70% > > 60% > > 50% > > 40% > > 30% > > 20% > > 10% > > 1% > > > > > > Each menu item would call cpu_throttle_set(). The value sent to this > > function would > > be determined like this: > > speed = -1 * menu_number + 100; > > ok, that is the info I was looking for. > > > speed would be sent to the cpu_throttle_set() function. This function would > > reduce > > the CPU usage of QEMU on the host. > > > > Why would someone want to slow down QEMU? > > - The user is using a laptop and don't want it to heat up. > > Sort-of makes sense, to keep the laptop quiet. > > > - The user wants to slow down a video game that is a little too challenging. > > Sure this would work? Throttling isn't a smooth slowdown, the cpu > continues to run at full speed and is forced to pause now and then. > > > - The user wants to save energy. > > Pointless. Laptop may run longer, but your job needs more time to > complete too. And constant vcpu start/stop isn't good to save power, > the cpus can't enter deep sleep states then because of the frequent > wakeups. > > > - The user wants to conduct some kind of stress test on a program and see > > how > > it handles under low cpu resources. > > Makes sense too. > > We already have "pause" in gtk, adding a "throttle" item next to it > looks reasonable to me. I don't think it is that useful to have 10% > steps in there, you probably never throttle 10% in practice. It's > probably more useful to have something like "throttle -> off / 50% / > 90% / 95% / 99%".
This feels like going down the slippery slope to turn the GTK frontend into a full mgmt UI, which is something we've said we don't want todo inside QEMU UI frontends. IMHO this kind of feature is best left to external mgmt layers, like virt-manager/GNOME Boxes/etc. It is already possible to timebox VMs CPU execution using cgroups quotas via libvirt. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|
