On 08.03.16 10:31:33, Ganapatrao Kulkarni wrote:

On Tue, Mar 8, 2016 at 1:17 AM, David Daney [off-list ref] wrote:

quoted

On 03/07/2016 11:22 AM, Robert Richter wrote:

quoted

On 03.03.16 15:55:35, David Daney wrote:

quoted

From: Ganapatrao Kulkarni <redacted>

Add DT bindings for numa mapping of memory, CPUs and IOs.

Reviewed-by: Robert Richter <redacted>
Signed-off-by: Ganapatrao Kulkarni <redacted>
Signed-off-by: David Daney <redacted>
---
  Documentation/devicetree/bindings/numa.txt | 272
+++++++++++++++++++++++++++++
  1 file changed, 272 insertions(+)
  create mode 100644 Documentation/devicetree/bindings/numa.txt

diff --git a/Documentation/devicetree/bindings/numa.txt

b/Documentation/devicetree/bindings/numa.txt
new file mode 100644
index 0000000..ec5ed7c

--- /dev/null
+++ b/Documentation/devicetree/bindings/numa.txt

quoted

+==============================================================================
+3 - distance-map

+==============================================================================
+
+The device tree node distance-map describes the relative
+distance (memory latency) between all numa nodes.
+
+- compatible : Should at least contain "numa-distance-map-v1".
+
+- 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.
+       The distances are equal in either direction.
+       2. The distance from a node to self (local distance) is
represented
+       with value 10 and all internode distance should be represented
with
+       a value greater than 10.
+       3. distance-matrix should have entries in lexicographical
ascending
+       order of nodes.
+       4. There must be only one device node distance-map which must
reside in the root node.

There is no note that this one is optional, but is it right? The
default is 10 for local and 20 for remote connections.

Do we need to explicitly state that it is optional?  Many node types are
optional, and their binding specifications don't really talk about their
being optional.

If the node is present then it has the meaning specified.

If the node is *not* present, then the special meaning described in the
bindings document does not apply.

In the case of NUMA, this means that all memory is equally distant (i.e. it
is *Uniform*), and we are not talking about a *Non* *Uniform* Memory
Architecture (NUMA) system.

quoted

If so, then ...

static int __init of_numa_parse_distance_map(void)
{
        int ret = -EINVAL;
        struct device_node *np = of_find_node_by_path("/distance-map");

        if (!np)
                return ret;

must return 0 instead of -EINVAL here.

No, I don't think doing that would be correct.

If there is no "distance-map", then of_numa_init() returns the error code.
This causes the code in arch/arm64/kernel/numa.c to fall back to the
non-NUMA "dummy_numa" case.

Which means distance-map is not optional for numa.

IMO, return 0 will allow 2 node system to have distance-map optional.
by default node distance is set to 10 for local node and for remote node is 20
and this will suffice the need of 2 node system.
by returning EINVAL, we are forcing 2 node system (and even for
systems which has equal remote distances)
to define distance-map.

This is exaclty the problem. numa_init() fails if there is no
distance-map node.

quoted

By adding your Reviewed-by: Robert Richter [off-list ref] tag to
patch 5/6, where we select between "real" and "dummy_numa", I had assumed
that you agreed with this approach.

This is from v6:

       if (strcmp(uname, "distance-map") != 0)
               return 0;

-Robert