From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Tue, 29 Jul 2014 15:04:12 +0100 Subject: [PATCH 19/19] Documentation: ACPI for ARM64 In-Reply-To: References: <1406206825-15590-1-git-send-email-hanjun.guo@linaro.org> <20140729112824.GM2576@leverpostej> <351673188.FxXsM7MvdA@wuerfel> <20140729130823.GP2576@leverpostej> Message-ID: <20140729140412.GR2576@leverpostej> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Jul 29, 2014 at 02:31:16PM +0100, Christoffer Dall wrote: > On 29 July 2014 15:08, Mark Rutland wrote: > > On Tue, Jul 29, 2014 at 01:52:40PM +0100, Arnd Bergmann wrote: > >> On Tuesday 29 July 2014 14:37:38 Christoffer Dall wrote: > >> > > >> > For reference, Red Hat's current arguing point for ACPI in VMs is > >> > hotplug of things like CPUs and memory for very large VMs, but I > >> > haven't thought too carefully about this just yet, as I don't have a > >> > 100+ core ARM 64-bit hardware lying around... > >> > >> I thought you could run guests with more virtual CPUs that you have > >> physical CPUs on the host. > >> > >> Regarding CPU and memory hotplug, don't we already have PSCI and > >> xen-balloon/virtio-balloon for that? > > > > PSCI (0.1) was there for guests from the start, and ACPI doesn't do > > anything different w.r.t. PSCI other than requiring PSCI 0.2 (which can > > be used by guests supporting only PSCI 0.1). So there's no magic for > > CPU hotplug provided by ACPI. > > With PSCI you can only provide your VM a bunch of CPUs and say that > they're all turned off, and then turn some of them on later. I > honestly don't know if you can do proper CPU hotplug with ACPI, but > the RH guys seem to argue that you can. Again, I didn't think too > carefully about this. Ah, I see. That would make some sense. > > > > Do either of the balloon drivers allow for memory to be hot-added to a > > system initially provisioned with less? > > > No, it's just about reclaiming memory. Same argument as above. Ok. Thanks for the clarifications. Cheers, Mark.