From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57584) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XmezL-0008L9-6C for qemu-devel@nongnu.org; Fri, 07 Nov 2014 03:33:53 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XmezD-0000wg-AI for qemu-devel@nongnu.org; Fri, 07 Nov 2014 03:33:47 -0500 Received: from mail-pd0-f171.google.com ([209.85.192.171]:57581) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XmezD-0000wI-4x for qemu-devel@nongnu.org; Fri, 07 Nov 2014 03:33:39 -0500 Received: by mail-pd0-f171.google.com with SMTP id r10so2907962pdi.2 for ; Fri, 07 Nov 2014 00:33:37 -0800 (PST) Message-ID: <545C835C.1010901@linaro.org> Date: Fri, 07 Nov 2014 16:31:24 +0800 From: Hanjun Guo MIME-Version: 1.0 References: <1414691045-4793-1-git-send-email-a.spyridakis@virtualopensystems.com> <20141030180216.GD31629@leverpostej> <545B1ACF.4090600@linaro.org> <545B9A7B.80101@redhat.com> In-Reply-To: <545B9A7B.80101@redhat.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [Linaro-acpi] [RFC PATCH 0/7] hw/arm/virt: Dynamic ACPI v5.1 table generation List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , Mark Rutland , Peter Maydell Cc: "tech@virtualopensystems.com" , QEMU Developers , "linaro-acpi@lists.linaro.org" 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