Hi, On Fri, Dec 11, 2015 at 08:11:07PM +0530, Ganapatrao Kulkarni wrote: > On Fri, Dec 11, 2015 at 7:23 PM, Mark Rutland <mark.rutland@xxxxxxx> wrote: > > 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. > thanks. [...] > >> +============================================================================== > >> +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. > ok, will do. [...] > >> +============================================================================== > >> +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? > AFAIK, it is to represent inter-node memory access latency. > > > >> +- compatible : Should at least contain "numa,distance-map-v1". > > > > Please use "numa-distance-map-v1", as "numa" is not a vendor. > ok > > > >> +- 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. > agreed, given that there is no know system to substantiate dual direction, > let us not explicit about direction. Regarding your comment in [1], I was expecting a respin of this series with the above comments addressed. I will not provide an ack until I've seen that. Additional concerns below also apply. > >> + 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? > this is based on representing local distance with 10 and > all inter-node latency being represented as multiple of 10. > > > > > Do we assume that a local access has value 1, e.g. each hop takes 20x a > > local access in this example? > The local distance is represented as 10, this is fixed and same as in ACPI. > Inter-node distance can be any number greater than 10. > this information can be added here to make it clear. This seems rather arbitrary. Why can we not define the local distance in the DT? I appreciate that the value is hard-coded for ACPI, but we don't have to copy that limitation. I'm not sure if asymmetric local distances matter. Thanks, Mark. [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-December/394634.html -- 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
