2:26 p.m.
On Thu, Apr 4, 2019 at 12:48 PM Brice Goglin <Brice.Goglin(a)inria.fr> wrote:
Hello
I am trying to understand the locality of the DAX devices with
respect to processors with SubNUMA clustering enabled. The machine
I am using has 6invalidate_mapping_pages proximity domains: #0-3 are the SNCs of both
processors, #4-5 are prox domains for each socket set of NVDIMMs.
SLIT says the topology looks like this, which seems OK to me:
Package 0 ---------- Package 1
NVregion0 NVregion1
| | | |
SNC 0 SNC 1 SNC 2 SNC 3
node0 node1 node2 node3
However each DAX "numa_node" attribute contains a single node ID,
which leads to this topology instead:
Package 0 ---------- Package 1
| | | |
SNC 0 SNC 1 SNC 2 SNC 3
node0 node1 node2 node3
| |
dax0.0 dax1.0
It looks like this is caused by acpi_map_pxm_to_online_node()
only returning the first closest node found in the SLIT.
However, even if we change it to return multiple local nodes,
the DAX "numa_node" attribute cannot expose multiple nodes.
Should we rather expose Keith HMAT attributes for DAX devices?
If I understand the suggestion correctly you're referring to the
"target_node" or the unique node number that gets assigned when the
memory is transitioned online. I struggle to see the incremental
benefit relative to what we lose with compatibility of the
"traditional" numa node interpretation for a device that indicates
which cpus are close to the given device. I think the bulk of the
problem is solved with the next suggestion below.
Maybe there's even a way to share them between DAX devices
and Dave's KMEM hotplugged NUMA nodes?
In this instance, where the expectation is that the NVDIMM range is
equidistant from both SNC nodes on a package, I would teach numactl
tool and other tooling to return a list of local nodes rather than the
single attribute. Effectively an operation like "numactl --preferred
block:pmem0" would return a node-mask that includes nodes 0 and 1.
By the way, I am not sure if my above configuration is what
we should expect on SNC-enabled production machines.
Is the NFIT table supposed to expose one SPA Range per SNC,
or one per socket? Should it depend with the SNC config in
the BIOS?
The NFIT is "supposed" to expose the interleave boundaries, and in
this case it seems to be saying that System RAM is interleaved
differently than the PMEM. Whether that is correct or not is for the
platform BIOS developer to validate. The OS is only equipped to trust
the SLIT.
If we had one SPA range per SNC, would it still be possible
to interleave NVDIMMs of both SNC to create a single region
for each socket?
I don't follow the question, if the SPA range is split you want the
SLIT to lie and say it isn't?
If I don't interleave NVDIMMs, I get the same result even if
some regions should be only local to node1 (or node3). Maybe
because they are still in the same SPA range, and thus still
get the entire range locality?
...or the SLIT is incorrect for that config.