On Tue, Oct 20, 2015 at 04:15:29PM +0530, Ganapatrao Kulkarni wrote:
> DT bindings for numa mapping of memory, cores and IOs.
>
> Reviewed-by: Robert Richter <rrichter@xxxxxxxxxx>
> Signed-off-by: Ganapatrao Kulkarni <gkulkarni@xxxxxxxxxxxxxxxxxx>
> ---
> Documentation/devicetree/bindings/arm/numa.txt | 275 +++++++++++++++++++++++++
> 1 file changed, 275 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..f3bc8e6
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/arm/numa.txt
> @@ -0,0 +1,275 @@
> +==============================================================================
> +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 - proximity
> +==============================================================================
> +The proximity device node property describes proximity domains within a
> +machine. This property can be used in device nodes like cpu, memory, bus and
> +devices to map to respective numa nodes.
> +
> +proximity property is a 32-bit integer which defines numa node id to which
> +this device node has numa proximity association.
> +
> +Example:
> + /* numa node 0 */
> + proximity = <0>;
> +
> + /* numa node 1 */
> + proximity = <1>;
It would probably be better to call this something like "numa-domain-id"
or "numa-node-id". The "proximity" is a relationship (that's actually
described in the distance map), and it makes it obvious that this is
NUMA related.
> +
> +==============================================================================
> +3 - distance-map
> +==============================================================================
> +
> +The device tree node distance-map describes the relative
> +distance (memory latency) between all numa nodes.
Rather than making this another magic name, we should give it a
compatible string. That will also help if/when updating this in future.
> +
> +- 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. If there is no distance-map, the system should setup:
> +
> + local/local: 10
> + local/remote: 20
> + for all node distances.
I think that either you have both the IDs and a distance map, or we
assume !NUMA (as we currently do). If your system is so trivial that the
above defaults are good enough, it's trivial to write them explicitly.
So I think this should go.
> +
> + 2. If both directions between 2 nodes have the same distance, only
> + one entry is required.
So there's a direction implied by each entry? That should be stated
explicitly.
That said, I'm having some difficulty comprehending an asymmetric
distance, and I worry that it's ill-defined.
What does the direction apply to specifically?
How is it to be interpreted?
Assuming I have two domains A and B, and I have:
distance-matrix = <A B 1>, <B A 255>;
What does that mean for those domains? What's fast and what is slow?
> + 3. distance-matrix shold have entries in ascending order of nodes.
s/ascending/lexicographical ascending/, and s/nodes/domain ids/, just to
be explicit.
> + 4. Device node distance-map must reside in the root node.
Presumably there should be no duplicate entries? We should state that
explicitly.
> +
> +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
> +
> + and dt presentation for this distance matrix is,
> +
> + distance-map {
> + distance-matrix = <0 0 10>,
> + <0 1 20>,
> + <0 2 40>,
> + <0 3 20>,
> + <1 0 20>,
> + <1 1 10>,
> + <1 2 20>,
> + <1 3 40>,
> + <2 0 40>,
> + <2 1 20>,
> + <2 2 10>,
> + <2 3 20>,
> + <3 0 20>,
> + <3 1 40>,
> + <3 2 20>,
> + <3 3 10>;
> + };
> +
> +Note:
> + 1. The entries like <0 0> <1 1> <2 2> <3 3>
> + can be optional and system can put default value(local distance, i.e 10).
As mentioned above, I think this should go.
Other than the comments above, this is looking promising!
Thanks,
Mark.
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