Re: [Qemu-devel] [PATCH v3 22/32] nvdimm: init the address region used by NVDIMM ACPI

[Igor Mammedov]

On Mon, 19 Oct 2015 18:01:17 +0800
Xiao Guangrong <address@hidden> wrote:

> 
> 
> On 10/19/2015 05:46 PM, Igor Mammedov wrote:
> > On Mon, 19 Oct 2015 12:17:22 +0300
> > "Michael S. Tsirkin" <address@hidden> wrote:
> >
> >> On Mon, Oct 19, 2015 at 03:44:13PM +0800, Xiao Guangrong wrote:
> >>>
> >>>
> >>> On 10/19/2015 03:39 PM, Michael S. Tsirkin wrote:
> >>>> On Mon, Oct 19, 2015 at 03:27:21PM +0800, Xiao Guangrong wrote:
> >>>>>>> +        nvdimm_init_memory_state(&pcms->nvdimm_memory,
> >>>>>>> system_memory, machine,
> >>>>>>> +                                 TARGET_PAGE_SIZE);
> >>>>>>> +
> >>>>>>
> >>>>>> Shouldn't this be conditional on presence of the nvdimm device?
> >>>>>>
> >>>>>
> >>>>> We will enable hotplug on nvdimm devices in the near future once
> >>>>> Linux driver is ready. I'd keep it here for future development.
> >>>>
> >>>> No, I don't think we should add stuff unconditionally. If not
> >>>> nvdimm, some other flag should indicate user intends to hotplug
> >>>> things.
> >>>>
> >>>
> >>> Actually, it is not unconditionally which is called if parameter
> >>> "-m aaa, maxmem=bbb" (aaa < bbb) is used. It is on the some path
> >>> of memoy-hotplug initiation.
> >>>
> >>
> >> Right, but that's not the same as nvdimm.
> >>
> >
> > it could be pc-machine property, then it could be turned on like
> > this: -machine nvdimm_support=on
> 
> Er, I do not understand why this separate switch is needed and why
> nvdimm and pc-dimm is different. :(
> 
> NVDIMM reuses memory-hotplug's framework, such as maxmem, slot, and
> dimm device, even some of ACPI logic to do hotplug things, etc. Both
> nvdimm and pc-dimm are built on the same infrastructure.
NVDIMM support consumes precious low RAM  and MMIO resources and
not small amount at that. So turning it on unconditionally with
memory hotplug even if NVDIMM wouldn't ever be used isn't nice.

However that concern could be dropped if instead of allocating it's
own control MMIO/RAM regions, NVDIMM would reuse memory hotplug's MMIO
region and replace RAM region with serializing/marshaling label data
over the same MMIO interface (yes, it's slower but it's not
performance critical path).  

> 
> 
> 
> 
> 
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