topology: Represent clusters of CPUs within a die

Both ACPI and DT provide the ability to describe additional layers of
topology between that of individual cores and higher level constructs
such as the level at which the last level cache is shared.
In ACPI this can be represented in PPTT as a Processor Hierarchy
Node Structure [1] that is the parent of the CPU cores and in turn
has a parent Processor Hierarchy Nodes Structure representing
a higher level of topology.

For example Kunpeng 920 has 6 or 8 clusters in each NUMA node, and each
cluster has 4 cpus. All clusters share L3 cache data, but each cluster
has local L3 tag. On the other hand, each clusters will share some
internal system bus.

+-----------------------------------+                          +---------+
|  +------+    +------+             +--------------------------+         |
|  | CPU0 |    | cpu1 |             |    +-----------+         |         |
|  +------+    +------+             |    |           |         |         |
|                                   +----+    L3     |         |         |
|  +------+    +------+   cluster   |    |    tag    |         |         |
|  | CPU2 |    | CPU3 |             |    |           |         |         |
|  +------+    +------+             |    +-----------+         |         |
|                                   |                          |         |
+-----------------------------------+                          |         |
+-----------------------------------+                          |         |
|  +------+    +------+             +--------------------------+         |
|  |      |    |      |             |    +-----------+         |         |
|  +------+    +------+             |    |           |         |         |
|                                   |    |    L3     |         |         |
|  +------+    +------+             +----+    tag    |         |         |
|  |      |    |      |             |    |           |         |         |
|  +------+    +------+             |    +-----------+         |         |
|                                   |                          |         |
+-----------------------------------+                          |   L3    |
                                                               |   data  |
+-----------------------------------+                          |         |
|  +------+    +------+             |    +-----------+         |         |
|  |      |    |      |             |    |           |         |         |
|  +------+    +------+             +----+    L3     |         |         |
|                                   |    |    tag    |         |         |
|  +------+    +------+             |    |           |         |         |
|  |      |    |      |             |    +-----------+         |         |
|  +------+    +------+             +--------------------------+         |
+-----------------------------------|                          |         |
+-----------------------------------|                          |         |
|  +------+    +------+             +--------------------------+         |
|  |      |    |      |             |    +-----------+         |         |
|  +------+    +------+             |    |           |         |         |
|                                   +----+    L3     |         |         |
|  +------+    +------+             |    |    tag    |         |         |
|  |      |    |      |             |    |           |         |         |
|  +------+    +------+             |    +-----------+         |         |
|                                   |                          |         |
+-----------------------------------+                          |         |
+-----------------------------------+                          |         |
|  +------+    +------+             +--------------------------+         |
|  |      |    |      |             |   +-----------+          |         |
|  +------+    +------+             |   |           |          |         |
|                                   |   |    L3     |          |         |
|  +------+    +------+             +---+    tag    |          |         |
|  |      |    |      |             |   |           |          |         |
|  +------+    +------+             |   +-----------+          |         |
|                                   |                          |         |
+-----------------------------------+                          |         |
+-----------------------------------+                          |         |
|  +------+    +------+             +--------------------------+         |
|  |      |    |      |             |  +-----------+           |         |
|  +------+    +------+             |  |           |           |         |
|                                   |  |    L3     |           |         |
|  +------+    +------+             +--+    tag    |           |         |
|  |      |    |      |             |  |           |           |         |
|  +------+    +------+             |  +-----------+           |         |
|                                   |                          +---------+
+-----------------------------------+

That means spreading tasks among clusters will bring more bandwidth
while packing tasks within one cluster will lead to smaller cache
synchronization latency. So both kernel and userspace will have
a chance to leverage this topology to deploy tasks accordingly to
achieve either smaller cache latency within one cluster or an even
distribution of load among clusters for higher throughput.

This patch exposes cluster topology to both kernel and userspace.
Libraried like hwloc will know cluster by cluster_cpus and related
sysfs attributes. PoC of HWLOC support at [2].

Note this patch only handle the ACPI case.

Special consideration is needed for SMT processors, where it is
necessary to move 2 levels up the hierarchy from the leaf nodes
(thus skipping the processor core level).

Note that arm64 / ACPI does not provide any means of identifying
a die level in the topology but that may be unrelate to the cluster
level.

[1] ACPI Specification 6.3 - section 5.2.29.1 processor hierarchy node
    structure (Type 0)
[2] https://github.com/hisilicon/hwloc/tree/linux-cluster

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210924085104.44806-2-21cnbao@gmail.com

1 files changed, 67 insertions, 0 deletions

diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index fe69dc518f31..701f61c01359 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -747,6 +747,73 @@ int find_acpi_cpu_topology_package(unsigned int cpu)
 }
 
 /**
+ * find_acpi_cpu_topology_cluster() - Determine a unique CPU cluster value
+ * @cpu: Kernel logical CPU number
+ *
+ * Determine a topology unique cluster ID for the given CPU/thread.
+ * This ID can then be used to group peers, which will have matching ids.
+ *
+ * The cluster, if present is the level of topology above CPUs. In a
+ * multi-thread CPU, it will be the level above the CPU, not the thread.
+ * It may not exist in single CPU systems. In simple multi-CPU systems,
+ * it may be equal to the package topology level.
+ *
+ * Return: -ENOENT if the PPTT doesn't exist, the CPU cannot be found
+ * or there is no toplogy level above the CPU..
+ * Otherwise returns a value which represents the package for this CPU.
+ */
+
+int find_acpi_cpu_topology_cluster(unsigned int cpu)
+{
+	struct acpi_table_header *table;
+	acpi_status status;
+	struct acpi_pptt_processor *cpu_node, *cluster_node;
+	u32 acpi_cpu_id;
+	int retval;
+	int is_thread;
+
+	status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
+	if (ACPI_FAILURE(status)) {
+		acpi_pptt_warn_missing();
+		return -ENOENT;
+	}
+
+	acpi_cpu_id = get_acpi_id_for_cpu(cpu);
+	cpu_node = acpi_find_processor_node(table, acpi_cpu_id);
+	if (cpu_node == NULL || !cpu_node->parent) {
+		retval = -ENOENT;
+		goto put_table;
+	}
+
+	is_thread = cpu_node->flags & ACPI_PPTT_ACPI_PROCESSOR_IS_THREAD;
+	cluster_node = fetch_pptt_node(table, cpu_node->parent);
+	if (cluster_node == NULL) {
+		retval = -ENOENT;
+		goto put_table;
+	}
+	if (is_thread) {
+		if (!cluster_node->parent) {
+			retval = -ENOENT;
+			goto put_table;
+		}
+		cluster_node = fetch_pptt_node(table, cluster_node->parent);
+		if (cluster_node == NULL) {
+			retval = -ENOENT;
+			goto put_table;
+		}
+	}
+	if (cluster_node->flags & ACPI_PPTT_ACPI_PROCESSOR_ID_VALID)
+		retval = cluster_node->acpi_processor_id;
+	else
+		retval = ACPI_PTR_DIFF(cluster_node, table);
+
+put_table:
+	acpi_put_table(table);
+
+	return retval;
+}
+
+/**
  * find_acpi_cpu_topology_hetero_id() - Get a core architecture tag
  * @cpu: Kernel logical CPU number
  *