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 <rrichter@xxxxxxxxxx> > Signed-off-by: Ganapatrao Kulkarni <gkulkarni@xxxxxxxxxxxxxxxxxx> 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. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
