On 2014-11-6 23:57, Paolo Bonzini wrote: > On 06/11/2014 07:53, Hanjun Guo wrote: >>> So the important question is _why_ the guest needs to see an ACPI >>> environment. What exactly can ACPI provide to the guest that DT does not >>> already provide, and why is that necessary? What infrastrucutre is >>> needed for that use case? >> >> There is important feature called system device dynamic reconfiguration, >> you know, hot-add/remove, if a gust need more/less memory or CPU, can we >> add or remove them dynamically with DT? ACPI can do this, but I have no >> idea if DT can. (Sorry, I don't know much about DT) > > Indeed hot-add/remove is the single biggest AML user in x86 QEMU. > Whether you really need it, it depends on what you are adding/removing. > > For PCI there is no problem. We can use PCIe from the beginning, and > use PCIe hotplug support that is already in QEMU. > > Memory and CPU are more problematic. For memory we could perhaps use a > PCI memory device, though I'm not sure if that would require drivers in > the OS or everything just works.
I didn't see some code for hot-adding system memory as PCI device, but people from Fujitsu is working on that in another solution - QEmu memory hot unplug support: https://www.mail-archive.com/qemu-devel@nongnu.org/msg251355.html for the guest, ACPI based memory hot-add/remove was already supported. Thanks Hanjun
