Re: [Qemu-devel] [PATCH v2 06/11] nvdimm acpi: initialize the resource used by NVDIMM ACPI

[Xiao Guangrong <guangrong.xiao@linux.intel.com>]

On 02/19/2016 04:08 PM, Michael S. Tsirkin wrote:
> On Thu, Feb 18, 2016 at 11:05:23AM +0100, Igor Mammedov wrote:
>> On Thu, 18 Feb 2016 12:03:36 +0800
>> Xiao Guangrong <guangrong.xiao@linux.intel.com> wrote:
>>
>>> On 02/18/2016 01:26 AM, Michael S. Tsirkin wrote:
>>>> On Wed, Feb 17, 2016 at 10:04:18AM +0800, Xiao Guangrong wrote:
>>>>>>>> As for the rest could that commands go via MMIO that we usually
>>>>>>>> use for control path?
>>>>>>>
>>>>>>> So both input data and output data go through single MMIO, we need to
>>>>>>> introduce a protocol to pass these data, that is complex?
>>>>>>>
>>>>>>> And is any MMIO we can reuse (more complexer？) or we should allocate this
>>>>>>> MMIO page （the old question - where to allocated?）?
>>>>>> Maybe you could reuse/extend memhotplug IO interface,
>>>>>> or alternatively as Michael suggested add a vendor specific PCI_Config,
>>>>>> I'd suggest PM device for that (hw/acpi/[piix4.c|ihc9.c])
>>>>>> which I like even better since you won't need to care about which ports
>>>>>> to allocate at all.
>>>>>
>>>>> Well, if Michael does not object, i will do it in the next version. :)
>>>>
>>>> Sorry, the thread's so long by now that I'm no longer sure what does "it" refer to.
>>>
>>> Never mind i saw you were busy on other loops.
>>>
>>> "It" means the suggestion of Igor that "map each label area right after each
>>> NVDIMM's data memory"
>> Michael pointed out that putting label right after each NVDIMM
>> might burn up to 256GB of address space due to DIMM's alignment for 256 NVDIMMs.
>> However if address for each label is picked with pc_dimm_get_free_addr()
>> and label's MemoryRegion alignment is default 2MB then all labels
>> would be allocated close to each other within a single 1GB range.
>>
>> That would burn only 1GB for 500 labels which is more than possible 256 NVDIMMs.
>
> I thought about it, once we support hotplug, this means that one will
> have to pre-declare how much is needed so QEMU can mark the correct
> memory reserved, that would be nasty. Maybe we always pre-reserve 1Gbyte.
> Okay but next time we need something, do we steal another Gigabyte?
> It seems too much, I'll think it over on the weekend.
>

It sounds like this approach (reserve-and-allocate) is very similar as the
old propose that dynamically allocates memory from the end of hotplug-mem. :)