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Re: [Qemu-devel] SMBIOS vs. NUMA (was: Build full type 19 tables)

From: Igor Mammedov
Subject: Re: [Qemu-devel] SMBIOS vs. NUMA (was: Build full type 19 tables)
Date: Thu, 13 Mar 2014 16:36:12 +0100

On Thu, 13 Mar 2014 10:37:52 -0400
"Gabriel L. Somlo" <address@hidden> wrote:

> On Thu, Mar 13, 2014 at 09:04:52AM +0100, Gerd Hoffmann wrote:
> >> Should we just assert((ram_size >> 10) < 0x80000000), and officially
> >> limit guests to < 2T ?
> > No.  Not fully sure what reasonable behavier would be in case more than
> > 2T are present.  I guess either not generating type16 entries at all or
> > simply fill in the maximum value we can represent.
> Well, there's an "extended maximum capacity" field available starting
> with smbios v2.7, which is an uint64_t counting bytes. Bumping the few
> other types up to 2.7 shouldn't be too onerous, but I have no idea how
> well the various currently supported OSs would react to smbios suddenly
> going v2.7...
> > > Then, a type20 node is assigned to the sub-4G portion of the first
> > > Type17 "device", and another type20 node is assigned to the over-4G
> > > portion of the same.
> > > 
> > > From then on, type20 nodes correspond to the rest of the 16G-or-less
> > > type17 devices pretty much on a 1:1 basis.
> > 
> > Hmm, not sure why type20 entries are handled the way they are.  I think
> > it would make more sense to have one type20 entry per e820 ram entry,
> > similar to type19.
> Type20 entries have pointers to type17 (memory_device_handle) and
> type19 (memory_array_mapped_address_handle). Which, if you turn it
> upside down could be interpreted as "every type 17 dimm needs (at
> least) a type20 device mapped address to point at it".
> > > If the e820 table will contain more than just two E820_RAM entries,
> > > and therefore we'll have more than the two Type19 nodes on the bottom
> > > row, what are the rules for extending the rest of the figure
> > > accordingly (i.e. how do we hook together more Type17 and Type20 nodes
> > > to go along with the extra Type19 nodes) ?
> > 
> > See above for type19+20.  type17 represents the dimms, so where the
> > memory is actually mapped doesn't matter there.  Lets simply sum up all
> > memory, then split into 16g pieces and create a type17 entry for each
> > piece.  At least initially.
> That's pretty much what happens now. If we decide to use e820 instead
> of simply (below_4g, above_4g), I'd like add some sort of assertion
> that would alert anyone who might start adding extra entries into e820
> beyond the current two (below_4g and above_4g) :)

After memory hotplug is in I might add e820 entries after above_4g
for present at boot hotpluggable DIMMDevices. They would have 1:1 mapping
i.e. t19<-t20<-t17 and belong only to 1 node.

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