Re: [Qemu-devel] [PATCH 1/2] pc-dimm: No numa option shouldn't break hotplug memory feature

[Tang Chen <tangchen@cn.fujitsu.com>]

On 09/23/2014 06:11 PM, zhanghailiang wrote:
> On 2014/9/23 16:58, Tang Chen wrote:
>>
>> On 09/23/2014 04:40 PM, Igor Mammedov wrote:
>>> ......
>>> It's fine to use SRAT for these purposes on baremetal NUMA systems 
>>> since
>>> due to used chipset constrains it's possible statically allocate ranges
>>> for every possible DIMM socket.
>>> However SRAT(which is optional table BTW) entries are not mandatory
>>> and override-able by ACPI Device's _PXM/_CRS methods replacing needs
>>> for SRAT entries and QEMU uses this fact by supplying these methods.
>>> QEMU adds FAKE SRAT entry only to workaround Windows limitation,
>>> and for nothing else.
>>>
>>> I think Linux does not violate ACPI spec and behaves as expected, 
>>> moreover
>>> it's more correct than Windows since memory hotplug will work on non 
>>> NUMA
>>> machines as well.
>>>
>>> Hence I think this patch is correct and allows memory hotplug in 
>>> absence
>>> of NUMA configuration. It also would allow to use pc-dimm as 
>>> replacement
>>> for initial memory for non-NUMA configs (which is on my TODO list)
>>>
>>> As for the Windows, QEMU has no idea what OS it would be running,
>>> I see 2 ways to solve issue:
>>>   1. user should know that memory hotplug on Windows requires NUMA 
>>> machine
>>>      and specify "-numa ..." option for this case.
>>>     (I've discussed this with libvirt folks and was promised that
>>>      if user enables memory hotplug, libvirt would provide "-numa" 
>>> option
>>>      to workaround Windows issue)
>>>
>>>   2. QEMU could unconditionally create single NUMA if memory hotplug is
>>>      enabled. (but that should be enable only for 2.2 or late machines
>>>      to avoid migration issues)
>>>
>> I prefer 2. I'll try to send patches for it if Zhang is also OK with it.
>>
>
> Yep, It is a good scheme to create a dummy NUMA unconditionally.
> But Igor has said there are migration issues for this scenario, do you 
> know what's
> it? ;)

Not sure.  This one ?

https://www.mail-archive.com/qemu-devel%40nongnu.org/msg249146.html

Thanks. :)

>
> .
>