The empty NUMA node, where no memory resides, are allowed. For
example, the following command line specifies two empty NUMA nodes.
With this, QEMU fails to boot because of the conflicting device-tree
node names, as the following error message indicates.
/home/gavin/sandbox/qemu.main/build/qemu-system-aarch64 \
-accel kvm -machine virt,gic-version=host \
-cpu host -smp 4,sockets=2,cores=2,threads=1 \
-m 1024M,slots=16,maxmem=64G \
-object memory-backend-ram,id=mem0,size=512M \
-object memory-backend-ram,id=mem1,size=512M \
-numa node,nodeid=0,cpus=0-1,memdev=mem0 \
-numa node,nodeid=1,cpus=2-3,memdev=mem1 \
-numa node,nodeid=2 \
-numa node,nodeid=3
:
qemu-system-aarch64: FDT: Failed to create subnode /memory@80000000:
FDT_ERR_EXISTS
As specified by linux device-tree binding document, the device-tree
nodes for these empty NUMA nodes shouldn't be generated. However,
the corresponding NUMA node IDs should be included in the distance
map. The memory hotplug through device-tree on ARM64 isn't existing
so far and it's not necessary to require the user to provide a distance
map. Furthermore, the default distance map Linux generates may even be
sufficient. So this simply skips populating the device-tree nodes for
these empty NUMA nodes to avoid the error, so that QEMU can be started
successfully.
Signed-off-by: Gavin Shan <gshan@redhat.com>
---
v5: Improved commit log and comments as Drew suggested.