On 04/23/2014 05:04 AM, Nishanth Aravamudan wrote:
> On 22.04.2014 [19:27:51 +1000], Benjamin Herrenschmidt wrote:
>> On Tue, 2014-04-22 at 19:12 +1000, Alexey Kardashevskiy wrote:
>>> I already have in plan to fix non-power-of-two sized memory nodes so I will
>>> this too.
>>>
>>> What exactly is the point in having NUMA memoryless nodes now? We do
>>> not support memory hotplug yet and balloon is not memory hotplug at
>>> all.
>>
>> It exists on real HW an it's always causing funny bugs, so being able to
>> simulate it in qemu would make it easier to test & debug.
>
> Yes, my primary purpose here is to help test & debug issues I see in
> other environments.
>
>>> And I still fail to see how the patch is wrong. May be the idea of
>>> having DT memory nodes the same thing as NUMA memory nodes is not
>>> the best one, but the patch is not changing that.
>
> No, but it does make it an error for the RMA not be in node0.
>
> + if (spapr->rma_size > node0_size) {
> + fprintf(stderr, "Error: Numa node 0 has to span the RMA
> (%#08"HWADDR_PR
> + spapr->rma_size);
> + exit(1);
> + }
>
> which will never be the case if node0 has no memory?
Except reproducing "funny" bugs from some real hardware, is there any other
point in memory-less nodes?
> I'm fine with the change being left in, I guess, I just want to make
> sure the semantics are intended.
It is intended. What does make you think that it is not taking into account
that _now_ memory nodes are equal to NUMA nodes in SPAPR's QEMU?
I am really confused.
>
> FWIW, if one instead tries to specify node 1 as memoryless, and nodes 0
> and 2 as having memory:
>
> sprintf(mem_name, "memory@" TARGET_FMT_lx, mem_start);
> off = fdt_add_subnode(fdt, 0, mem_name);
> _FDT(off);
>
> ends up getting a duplicate error from _FDT because we're trying
> to create memory@<end of node 0> twice, once for node 1 and once for
> node 2. I'm not actually sure what we're supposed to do in that
> situation. Looking at a PowerVM LPAR with the following topology [1]:
>
> numactl --hardware
> available: 3 nodes (1-3)
> node 1 cpus: 0 1 2 3 4 5 6 7 8 9 10 11
> node 1 size: 0 MB
> node 1 free: 0 MB
> node 2 cpus:
> node 2 size: 7935 MB
> node 2 free: 7302 MB
> node 3 cpus:
> node 3 size: 8396 MB
> node 3 free: 8338 MB
> node distances:
> node 1 2 3
> 1: 10 20 20
> 2: 20 10 20
> 3: 20 20 10
>
> I only see /proc/device-tree/memory@0. Perhaps the node 2 and node 3 are
> from ibm,dynamic-reconfiguration-memory?
It would help if you told how exactly you run QEMU.
>
> Thanks,
> Nish
>
> [1] Running a hacked kernel that doesn't require node 0 to be present in
> the first place.
>
--
Alexey
