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 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.

Thanks. :)