On Thu, 2009-09-24 at 18:38 +1000, Benjamin Herrenschmidt wrote: > On Thu, 2009-09-24 at 09:51 +0200, Peter Zijlstra wrote: > > > I don't quite follow your logic here. This is useful for more than just > > > hypervisors. For example, take the HV out of the picture for a moment > > > and imagine that the HW has the ability to offline CPU in various power > > > levels, with varying latencies to bring them back. > > > > cpu-hotplug is an utter slow path, anybody saying latency and hotplug in > > the same sentence doesn't seem to grasp either or both concepts. > > Let's forget about latency then. Let's imagine I want to set a CPU > offline to save power, vs. setting it offline -and- opening the back > door of the machine to actually physically replace it :-)
If the hardware is capable of physical hotplug, then surely powering the socket down saves most power and is the preferred mode? > In any case, I don't see the added feature as being problematic, and > not such a "layering violation" as you seem to imply it is. It's a > convenient way to atomically take the CPU out -and- convey some > information about the "intent" to the hypervisor, and I really fail > to see why you have so strong objections about it. Ignorance on my part probably :-) I'm simply not seeing a use case for it, except for the virt case, which I think we should bug the virt interface with and not the cpu-hotplug interface. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
