Re: [Qemu-ppc] [Qemu-devel] [PATCH 0/7] spapr: rework memory nodes

[Eduardo Habkost]

On Mon, Jun 16, 2014 at 06:16:29PM +1000, Alexey Kardashevskiy wrote:
> On 06/16/2014 05:53 PM, Alexey Kardashevskiy wrote:
> > c4177479 "spapr: make sure RMA is in first mode of first memory node"
> > introduced regression which prevents from running guests with memoryless
> > NUMA node#0 which may happen on real POWER8 boxes and which would make
> > sense to debug in QEMU.
> > 
> > This patchset aim is to fix that and also fix various code problems in
> > memory nodes generation.
> > 
> > These 2 patches could be merged (the resulting patch looks rather ugly):
> > spapr: Use DT memory node rendering helper for other nodes
> > spapr: Move DT memory node rendering to a helper
> > 
> > Please comment. Thanks!
> > 
> 
> Sure I forgot to add an example of what I am trying to run without errors
> and warnings:
> 
> /home/aik/qemu-system-ppc64 \
> -enable-kvm \
> -machine pseries \
> -nographic \
> -vga none \
> -drive id=id0,if=none,file=virtimg/fc20_24GB.qcow2,format=qcow2 \
> -device scsi-disk,id=id1,drive=id0 \
> -m 2080 \
> -smp 8 \
> -numa node,nodeid=0,cpus=0-7,memory=0 \
> -numa node,nodeid=2,cpus=0-3,mem=1040 \
> -numa node,nodeid=4,cpus=4-7,mem=1040

(Note: I will ignore the "cpus" argument for the discussion below.)

I understand now that the non-contiguous node IDs are guest-visible.

But I still would like to understand the motivations for your use case,
to understand which solution makes more sense.

If you really want 5 nodes, you just need to write this:
  -numa node,nodeid=0,cpus=0-7,memory=0 \
  -numa node,nodeid=1 \
  -numa node,nodeid=2,cpus=0-3,mem=1040 \
  -numa node,nodeid=3 \
  -numa node,nodeid=4,cpus=4-7,mem=1040

If you just want 3 nodes, you can just write this:
  -numa node,nodeid=0,cpus=0-7,memory=0 \
  -numa node,nodeid=1,cpus=0-3,mem=1040 \
  -numa node,nodeid=4,cpus=4-7,mem=1040

But you seem to claim you need 3 nodes with non-contiguous IDs. In that
case, which exactly is the guest-visible difference you expect to get
between:
  -numa node,nodeid=0,cpus=0-7,memory=0 \
  -numa node,nodeid=1 \
  -numa node,nodeid=2,cpus=0-3,mem=1040 \
  -numa node,nodeid=3 \
  -numa node,nodeid=4,cpus=4-7,mem=1040
and
  -numa node,nodeid=0,cpus=0-7,memory=0 \
  -numa node,nodeid=2,cpus=0-3,mem=1040 \
  -numa node,nodeid=4,cpus=4-7,mem=1040
?

Because your patch is making both be exactly the same, and I guess you
don't want that (otherwise you could simply use the 5-node command-line
above and we wouldn't need patch 7/7).

-- 
Eduardo