Hi,
On Tue, Nov 17, 2015 at 10:50:41PM +0530, Ganapatrao Kulkarni wrote:
> DT bindings for numa mapping of memory, cores and IOs.
>
> Reviewed-by: Robert Richter <[email protected]>
> Signed-off-by: Ganapatrao Kulkarni <[email protected]>
Overall this looks good to me. However, I have a couple of concerns.
> ---
> Documentation/devicetree/bindings/arm/numa.txt | 272
> +++++++++++++++++++++++++
> 1 file changed, 272 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/arm/numa.txt
>
> diff --git a/Documentation/devicetree/bindings/arm/numa.txt
> b/Documentation/devicetree/bindings/arm/numa.txt
> new file mode 100644
> index 0000000..b87bf4f
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/numa.txt
> @@ -0,0 +1,272 @@
> +==============================================================================
> +NUMA binding description.
> +==============================================================================
> +
> +==============================================================================
> +1 - Introduction
> +==============================================================================
> +
> +Systems employing a Non Uniform Memory Access (NUMA) architecture contain
> +collections of hardware resources including processors, memory, and I/O
> buses,
> +that comprise what is commonly known as a NUMA node.
> +Processor accesses to memory within the local NUMA node is generally faster
> +than processor accesses to memory outside of the local NUMA node.
> +DT defines interfaces that allow the platform to convey NUMA node
> +topology information to OS.
> +
> +==============================================================================
> +2 - numa-node-id
> +==============================================================================
> +The device node property numa-node-id describes numa domains within a
> +machine. This property can be used in device nodes like cpu, memory, bus and
> +devices to map to respective numa nodes.
> +
> +numa-node-id property is a 32-bit integer which defines numa node id to which
> +this device node has numa domain association.
I'd prefer if the above two paragraphs were replaced with:
For the purpose of identification, each NUMA node is associated
with a unique token known as a node id. For the purpose of this
binding a node id is a 32-bit integer.
A device node is associated with a NUMA node by the presence of
a numa-node-id property which contains the node id of the
device.
> +
> +Example:
> + /* numa node 0 */
> + numa-node-id = <0>;
> +
> + /* numa node 1 */
> + numa-node-id = <1>;
> +
> +==============================================================================
> +3 - distance-map
> +==============================================================================
> +
> +The device tree node distance-map describes the relative
> +distance (memory latency) between all numa nodes.
Is this not a combined approximation for latency and bandwidth?
> +- compatible : Should at least contain "numa,distance-map-v1".
Please use "numa-distance-map-v1", as "numa" is not a vendor.
> +- distance-matrix
> + This property defines a matrix to describe the relative distances
> + between all numa nodes.
> + It is represented as a list of node pairs and their relative distance.
> +
> + Note:
> + 1. Each entry represents distance from first node to second node.
> + 2. If both directions between 2 nodes have the same distance, only
> + one entry is required.
I still don't understand what direction means in this context. Are there
systems (of any architecture) which don't have symmetric distances?
Which accesses does this apply differently to?
Given that, I think that it might be best to explicitly call out
distances as being equal, and leave any directionality for a later
revision of the binding when we have some semantics for directionality.
> + 2. distance-matrix shold have entries in lexicographical ascending
> order of nodes.
> + 3. There must be only one Device node distance-map and must reside in
> the root node.
> +
> +Example:
> + 4 nodes connected in mesh/ring topology as below,
> +
> + 0_______20______1
> + | |
> + | |
> + 20| |20
> + | |
> + | |
> + |_______________|
> + 3 20 2
> +
> + if relative distance for each hop is 20,
> + then inter node distance would be for this topology will be,
> + 0 -> 1 = 20
> + 1 -> 2 = 20
> + 2 -> 3 = 20
> + 3 -> 0 = 20
> + 0 -> 2 = 40
> + 1 -> 3 = 40
How is this scaled relative to a local access?
Do we assume that a local access has value 1, e.g. each hop takes 20x a
local access in this example?
Do we need a finer-grained scale (e.g. to allow us to represent a
distance of 2.5)? The ACPI SLIT spec seems to give local accesses a
value 10 implicitly to this end.
Other than those points, I'm happy with this binding.
Thanks,
Mark.
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