On Mon, Jan 11, 2010 at 6:32 PM, Gleb Natapov <gleb@xxxxxxxxxx> wrote: > On Mon, Jan 11, 2010 at 06:24:32PM +0900, Ryota Ozaki wrote: >> 2010/1/10 Gleb Natapov <gleb@xxxxxxxxxx>: [...] >> > May I ask what do you need it for? >> >> Oh sorry, actually I have not so strong desire on cpu hotplug but >> I have on memory hotplug and just want to learn stuffs to implement >> it from cpu's one. Honestly said I'm not sure someone want it. > Hmm, everybody want it, but nobody can't say why. Looks like it just > sounds cool :) I cannot disclaim that :) If we have textbookish answers, they will be somewhat "We have a physical machine could have multiple VMs and the number of VMs dynamically varies, so we need to change the number of VCPUs of the VMs on the fly to gain maximum throughput" or "A migrated VM may have an opportunity to get more VCPUs so far because the destination physical machine has more number of CPUs than source one.", however, I have not ever faced such situations. >> >> > The problem is that there is no standard >> > way to hotplug CPUs in a PC. Linux implements the way UNISYS happen to do >> > it, but no other system do it like that. Windows implements it >> > differently and in the way that conflicts with Linux, so you can't >> > have working Linux implementation and pass Microsoft SVVP test at the >> > same time for instance. >> >> Could I ask you what's the difference between the two implementations? > I have no idea how it works in Windows. It seems that some kind of > driver is required for hot-plugging cpu there. I see. Thanks. I'll check it and also VMware case that likely supports the function. > >> Don't we have a possibility to have different implementations in qemu-kvm >> (and SeaBIOS)? > What do you mean by different implementation? Different one for Windows > and Linux and have a switch to choose one? Possible, but not desirable. > Different from what we had in BOCHS BIOS? Also possible, but will > require changes to Linux kernel and older Kernel will not work. I mean the former one. I think it'd be a way to have cpu hotplug supports for both Linxu and Windows (and others), but yes, it's the case only if the supports are really really desired. So I want to hear the comments by someones using CPU hotplug functions in real use if exist. > >> And also I want to ask that the problem can be applied >> to memory hotplug case? >> > AFAIK memory hotplug is part of ACPI spec and if implemented correctly > should not cause any problems. That makes me happy ;-) Thank you for telling me! ozaki-r > > -- > Gleb. > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
