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SubjectRe: [PATCH v6 1/7] Documentation: DT: arm: add support for sockets defining package boundaries
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On 5/29/19 5:13 PM, Atish Patra wrote:
> From: Sudeep Holla <sudeep.holla@arm.com>
>
> The current ARM DT topology description provides the operating system
> with a topological view of the system that is based on leaf nodes
> representing either cores or threads (in an SMT system) and a
> hierarchical set of cluster nodes that creates a hierarchical topology
> view of how those cores and threads are grouped.
>
> However this hierarchical representation of clusters does not allow to
> describe what topology level actually represents the physical package or
> the socket boundary, which is a key piece of information to be used by
> an operating system to optimize resource allocation and scheduling.
>

Are physical package descriptions really needed? What does "socket"
imply that a higher layer "cluster" node grouping does not? It doesn't
imply a different NUMA distance and the definition of "socket" is
already not well defined, is a dual chiplet processor not just a fancy
dual "socket" or are dual "sockets" on a server board "slotket" card,
will we need new names for those too..

Andrew

> Lets add a new "socket" node type in the cpu-map node to describe the
> same.
>
> Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
> Reviewed-by: Rob Herring <robh@kernel.org>
> ---
> .../devicetree/bindings/arm/topology.txt | 52 ++++++++++++++-----
> 1 file changed, 39 insertions(+), 13 deletions(-)
>
> diff --git a/Documentation/devicetree/bindings/arm/topology.txt b/Documentation/devicetree/bindings/arm/topology.txt
> index b0d80c0fb265..3b8febb46dad 100644
> --- a/Documentation/devicetree/bindings/arm/topology.txt
> +++ b/Documentation/devicetree/bindings/arm/topology.txt
> @@ -9,6 +9,7 @@ ARM topology binding description
> In an ARM system, the hierarchy of CPUs is defined through three entities that
> are used to describe the layout of physical CPUs in the system:
>
> +- socket
> - cluster
> - core
> - thread
> @@ -63,21 +64,23 @@ nodes are listed.
>
> The cpu-map node's child nodes can be:
>
> - - one or more cluster nodes
> + - one or more cluster nodes or
> + - one or more socket nodes in a multi-socket system
>
> Any other configuration is considered invalid.
>
> -The cpu-map node can only contain three types of child nodes:
> +The cpu-map node can only contain 4 types of child nodes:
>
> +- socket node
> - cluster node
> - core node
> - thread node
>
> whose bindings are described in paragraph 3.
>
> -The nodes describing the CPU topology (cluster/core/thread) can only
> -be defined within the cpu-map node and every core/thread in the system
> -must be defined within the topology. Any other configuration is
> +The nodes describing the CPU topology (socket/cluster/core/thread) can
> +only be defined within the cpu-map node and every core/thread in the
> +system must be defined within the topology. Any other configuration is
> invalid and therefore must be ignored.
>
> ===========================================
> @@ -85,26 +88,44 @@ invalid and therefore must be ignored.
> ===========================================
>
> cpu-map child nodes must follow a naming convention where the node name
> -must be "clusterN", "coreN", "threadN" depending on the node type (ie
> -cluster/core/thread) (where N = {0, 1, ...} is the node number; nodes which
> -are siblings within a single common parent node must be given a unique and
> +must be "socketN", "clusterN", "coreN", "threadN" depending on the node type
> +(ie socket/cluster/core/thread) (where N = {0, 1, ...} is the node number; nodes
> +which are siblings within a single common parent node must be given a unique and
> sequential N value, starting from 0).
> cpu-map child nodes which do not share a common parent node can have the same
> name (ie same number N as other cpu-map child nodes at different device tree
> levels) since name uniqueness will be guaranteed by the device tree hierarchy.
>
> ===========================================
> -3 - cluster/core/thread node bindings
> +3 - socket/cluster/core/thread node bindings
> ===========================================
>
> -Bindings for cluster/cpu/thread nodes are defined as follows:
> +Bindings for socket/cluster/cpu/thread nodes are defined as follows:
> +
> +- socket node
> +
> + Description: must be declared within a cpu-map node, one node
> + per physical socket in the system. A system can
> + contain single or multiple physical socket.
> + The association of sockets and NUMA nodes is beyond
> + the scope of this bindings, please refer [2] for
> + NUMA bindings.
> +
> + This node is optional for a single socket system.
> +
> + The socket node name must be "socketN" as described in 2.1 above.
> + A socket node can not be a leaf node.
> +
> + A socket node's child nodes must be one or more cluster nodes.
> +
> + Any other configuration is considered invalid.
>
> - cluster node
>
> Description: must be declared within a cpu-map node, one node
> per cluster. A system can contain several layers of
> - clustering and cluster nodes can be contained in parent
> - cluster nodes.
> + clustering within a single physical socket and cluster
> + nodes can be contained in parent cluster nodes.
>
> The cluster node name must be "clusterN" as described in 2.1 above.
> A cluster node can not be a leaf node.
> @@ -164,13 +185,15 @@ Bindings for cluster/cpu/thread nodes are defined as follows:
> 4 - Example dts
> ===========================================
>
> -Example 1 (ARM 64-bit, 16-cpu system, two clusters of clusters):
> +Example 1 (ARM 64-bit, 16-cpu system, two clusters of clusters in a single
> +physical socket):
>
> cpus {
> #size-cells = <0>;
> #address-cells = <2>;
>
> cpu-map {
> + socket0 {
> cluster0 {
> cluster0 {
> core0 {
> @@ -253,6 +276,7 @@ cpus {
> };
> };
> };
> + };
>
> CPU0: cpu@0 {
> device_type = "cpu";
> @@ -473,3 +497,5 @@ cpus {
> ===============================================================================
> [1] ARM Linux kernel documentation
> Documentation/devicetree/bindings/arm/cpus.yaml
> +[2] Devicetree NUMA binding description
> + Documentation/devicetree/bindings/numa.txt
>

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