[RFC PATCH] topology: Represent clusters of CPUs within a die.

From: Jonathan Cameron
Date: Fri Oct 16 2020 - 11:27:35 EST

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 clusters of 4 CPUs. These do not share
any cache resources, but the interconnect topology is such that
the cost to transfer ownership of a cacheline between CPUs within
a cluster is lower than between CPUs in different clusters on the same
die. Hence, it can make sense to deliberately schedule threads
sharing data to a single cluster.

This patch simply exposes this information to userspace libraries
like hwloc by providing 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).

Currently the ID provided is the offset of the Processor
Hierarchy Nodes Structure within PPTT. Whilst this is unique
it is not terribly elegant so alternative suggestions welcome.

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.

RFC questions:
1) Naming
2) Related to naming, do we want to represent all potential levels,
or this enough? On Kunpeng920, the next level up from cluster happens
to be covered by llc cache sharing, but in theory more than one
level of cluster description might be needed by some future system.
3) Do we need DT code in place? I'm not sure any DT based ARM64
systems would have enough complexity for this to be useful.
4) Other architectures? Is this useful on x86 for example?

[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@xxxxxxxxxx>
---

Documentation/admin-guide/cputopology.rst | 26 ++++++++--
arch/arm64/kernel/topology.c | 2 +
drivers/acpi/pptt.c | 60 +++++++++++++++++++++++
drivers/base/arch_topology.c | 14 ++++++
drivers/base/topology.c | 10 ++++
include/linux/acpi.h | 5 ++
include/linux/arch_topology.h | 5 ++
include/linux/topology.h | 6 +++
8 files changed, 124 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/cputopology.rst b/Documentation/admin-guide/cputopology.rst
index b90dafcc8237..f9d374560047 100644
--- a/Documentation/admin-guide/cputopology.rst
+++ b/Documentation/admin-guide/cputopology.rst
@@ -24,6 +24,12 @@ core_id:
identifier (rather than the kernel's). The actual value is
architecture and platform dependent.

+cluster_id:
+
+ the Cluster ID of cpuX. Typically it is the hardware platform's
+ identifier (rather than the kernel's). The actual value is
+ architecture and platform dependent.
+
book_id:

the book ID of cpuX. Typically it is the hardware platform's
@@ -56,6 +62,14 @@ package_cpus_list:
human-readable list of CPUs sharing the same physical_package_id.
(deprecated name: "core_siblings_list")

+cluster_cpus:
+
+ internal kernel map of CPUs within the same cluster.
+
+cluster_cpus_list:
+
+ human-readable list of CPUs within the same cluster.
+
die_cpus:

internal kernel map of CPUs within the same die.
@@ -96,11 +110,13 @@ these macros in include/asm-XXX/topology.h::

#define topology_physical_package_id(cpu)
#define topology_die_id(cpu)
+ #define topology_cluster_id(cpu)
#define topology_core_id(cpu)
#define topology_book_id(cpu)
#define topology_drawer_id(cpu)
#define topology_sibling_cpumask(cpu)
#define topology_core_cpumask(cpu)
+ #define topology_cluster_cpumask(cpu)
#define topology_die_cpumask(cpu)
#define topology_book_cpumask(cpu)
#define topology_drawer_cpumask(cpu)
@@ -116,10 +132,12 @@ not defined by include/asm-XXX/topology.h:

1) topology_physical_package_id: -1
2) topology_die_id: -1
-3) topology_core_id: 0
-4) topology_sibling_cpumask: just the given CPU
-5) topology_core_cpumask: just the given CPU
-6) topology_die_cpumask: just the given CPU
+3) topology_cluster_id: -1
+4) topology_core_id: 0
+5) topology_sibling_cpumask: just the given CPU
+6) topology_core_cpumask: just the given CPU
+7) topology_cluster_cpumask: just the given CPU
+8) topology_die_cpumask: just the given CPU

For architectures that don't support books (CONFIG_SCHED_BOOK) there are no
default definitions for topology_book_id() and topology_book_cpumask().
diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index 0801a0f3c156..4c40240fdf6a 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -101,6 +101,8 @@ int __init parse_acpi_topology(void)
cpu_topology[cpu].thread_id = -1;
cpu_topology[cpu].core_id = topology_id;
}
+ topology_id = find_acpi_cpu_topology_cluster(cpu);
+ cpu_topology[cpu].cluster_id = topology_id;
topology_id = find_acpi_cpu_topology_package(cpu);
cpu_topology[cpu].package_id = topology_id;

diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index 4ae93350b70d..8646a93e4348 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -736,6 +736,66 @@ int find_acpi_cpu_topology_package(unsigned int cpu)
ACPI_PPTT_PHYSICAL_PACKAGE);
}

+/**
+ * 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;
+ int retval;
+ int is_thread;
+
+ status = acpi_get_table(ACPI_SIG_PPTT, 0, &table);
+ if (ACPI_FAILURE(status)) {
+ acpi_pptt_warn_missing();
+ return -ENOENT;
+ }
+ cpu_node = acpi_find_processor_node(table, cpu);
+ 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;
+ }
+ }
+ 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
diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 75f72d684294..e2ca8f39131e 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -497,6 +497,11 @@ const struct cpumask *cpu_coregroup_mask(int cpu)
return core_mask;
}

+const struct cpumask *cpu_clustergroup_mask(int cpu)
+{
+ return &cpu_topology[cpu].cluster_sibling;
+}
+
void update_siblings_masks(unsigned int cpuid)
{
struct cpu_topology *cpu_topo, *cpuid_topo = &cpu_topology[cpuid];
@@ -514,6 +519,11 @@ void update_siblings_masks(unsigned int cpuid)
if (cpuid_topo->package_id != cpu_topo->package_id)
continue;

+ if (cpuid_topo->cluster_id == cpu_topo->cluster_id) {
+ cpumask_set_cpu(cpu, &cpuid_topo->cluster_sibling);
+ cpumask_set_cpu(cpuid, &cpu_topo->cluster_sibling);
+ }
+
cpumask_set_cpu(cpuid, &cpu_topo->core_sibling);
cpumask_set_cpu(cpu, &cpuid_topo->core_sibling);

@@ -532,6 +542,9 @@ static void clear_cpu_topology(int cpu)
cpumask_clear(&cpu_topo->llc_sibling);
cpumask_set_cpu(cpu, &cpu_topo->llc_sibling);

+ cpumask_clear(&cpu_topo->cluster_sibling);
+ cpumask_set_cpu(cpu, &cpu_topo->cluster_sibling);
+
cpumask_clear(&cpu_topo->core_sibling);
cpumask_set_cpu(cpu, &cpu_topo->core_sibling);
cpumask_clear(&cpu_topo->thread_sibling);
@@ -562,6 +575,7 @@ void remove_cpu_topology(unsigned int cpu)
cpumask_clear_cpu(cpu, topology_core_cpumask(sibling));
for_each_cpu(sibling, topology_sibling_cpumask(cpu))
cpumask_clear_cpu(cpu, topology_sibling_cpumask(sibling));
+
for_each_cpu(sibling, topology_llc_cpumask(cpu))
cpumask_clear_cpu(cpu, topology_llc_cpumask(sibling));

diff --git a/drivers/base/topology.c b/drivers/base/topology.c
index ad8d33c6077b..f72ac9acc112 100644
--- a/drivers/base/topology.c
+++ b/drivers/base/topology.c
@@ -46,6 +46,9 @@ static DEVICE_ATTR_RO(physical_package_id);
define_id_show_func(die_id);
static DEVICE_ATTR_RO(die_id);

+define_id_show_func(cluster_id);
+static DEVICE_ATTR_RO(cluster_id);
+
define_id_show_func(core_id);
static DEVICE_ATTR_RO(core_id);

@@ -61,6 +64,10 @@ define_siblings_show_func(core_siblings, core_cpumask);
static DEVICE_ATTR_RO(core_siblings);
static DEVICE_ATTR_RO(core_siblings_list);

+define_siblings_show_func(cluster_cpus, cluster_cpumask);
+static DEVICE_ATTR_RO(cluster_cpus);
+static DEVICE_ATTR_RO(cluster_cpus_list);
+
define_siblings_show_func(die_cpus, die_cpumask);
static DEVICE_ATTR_RO(die_cpus);
static DEVICE_ATTR_RO(die_cpus_list);
@@ -88,6 +95,7 @@ static DEVICE_ATTR_RO(drawer_siblings_list);
static struct attribute *default_attrs[] = {
&dev_attr_physical_package_id.attr,
&dev_attr_die_id.attr,
+ &dev_attr_cluster_id.attr,
&dev_attr_core_id.attr,
&dev_attr_thread_siblings.attr,
&dev_attr_thread_siblings_list.attr,
@@ -95,6 +103,8 @@ static struct attribute *default_attrs[] = {
&dev_attr_core_cpus_list.attr,
&dev_attr_core_siblings.attr,
&dev_attr_core_siblings_list.attr,
+ &dev_attr_cluster_cpus.attr,
+ &dev_attr_cluster_cpus_list.attr,
&dev_attr_die_cpus.attr,
&dev_attr_die_cpus_list.attr,
&dev_attr_package_cpus.attr,
diff --git a/include/linux/acpi.h b/include/linux/acpi.h
index 159a461d8524..05b1e30f43fc 100644
--- a/include/linux/acpi.h
+++ b/include/linux/acpi.h
@@ -1333,6 +1333,7 @@ static inline int lpit_read_residency_count_address(u64 *address)
#ifdef CONFIG_ACPI_PPTT
int acpi_pptt_cpu_is_thread(unsigned int cpu);
int find_acpi_cpu_topology(unsigned int cpu, int level);
+int find_acpi_cpu_topology_cluster(unsigned int cpu);
int find_acpi_cpu_topology_package(unsigned int cpu);
int find_acpi_cpu_topology_hetero_id(unsigned int cpu);
int find_acpi_cpu_cache_topology(unsigned int cpu, int level);
@@ -1345,6 +1346,10 @@ static inline int find_acpi_cpu_topology(unsigned int cpu, int level)
{
return -EINVAL;
}
+static inline int find_acpi_cpu_topology_cluster(unsigned int cpu)
+{
+ return -EINVAL;
+}
static inline int find_acpi_cpu_topology_package(unsigned int cpu)
{
return -EINVAL;
diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
index 69b1dabe39dc..dba06864eab5 100644
--- a/include/linux/arch_topology.h
+++ b/include/linux/arch_topology.h
@@ -45,10 +45,12 @@ void topology_set_thermal_pressure(const struct cpumask *cpus,
struct cpu_topology {
int thread_id;
int core_id;
+ int cluster_id;
int package_id;
int llc_id;
cpumask_t thread_sibling;
cpumask_t core_sibling;
+ cpumask_t cluster_sibling;
cpumask_t llc_sibling;
};

@@ -56,13 +58,16 @@ struct cpu_topology {
extern struct cpu_topology cpu_topology[NR_CPUS];

#define topology_physical_package_id(cpu) (cpu_topology[cpu].package_id)
+#define topology_cluster_id(cpu) (cpu_topology[cpu].cluster_id)
#define topology_core_id(cpu) (cpu_topology[cpu].core_id)
#define topology_core_cpumask(cpu) (&cpu_topology[cpu].core_sibling)
#define topology_sibling_cpumask(cpu) (&cpu_topology[cpu].thread_sibling)
+#define topology_cluster_cpumask(cpu) (&cpu_topology[cpu].cluster_sibling)
#define topology_llc_cpumask(cpu) (&cpu_topology[cpu].llc_sibling)
void init_cpu_topology(void);
void store_cpu_topology(unsigned int cpuid);
const struct cpumask *cpu_coregroup_mask(int cpu);
+const struct cpumask *cpu_clustergroup_mask(int cpu);
void update_siblings_masks(unsigned int cpu);
void remove_cpu_topology(unsigned int cpuid);
void reset_cpu_topology(void);
diff --git a/include/linux/topology.h b/include/linux/topology.h
index 608fa4aadf0e..5f666488f8f1 100644
--- a/include/linux/topology.h
+++ b/include/linux/topology.h
@@ -185,6 +185,9 @@ static inline int cpu_to_mem(int cpu)
#ifndef topology_die_id
#define topology_die_id(cpu) ((void)(cpu), -1)
#endif
+#ifndef topology_cluster_id
+#define topology_cluster_id(cpu) ((void)(cpu), -1)
+#endif
#ifndef topology_core_id
#define topology_core_id(cpu) ((void)(cpu), 0)
#endif
@@ -194,6 +197,9 @@ static inline int cpu_to_mem(int cpu)
#ifndef topology_core_cpumask
#define topology_core_cpumask(cpu) cpumask_of(cpu)
#endif
+#ifndef topology_cluster_cpumask
+#define topology_cluster_cpumask(cpu) cpumask_of(cpu)
+#endif
#ifndef topology_die_cpumask
#define topology_die_cpumask(cpu) cpumask_of(cpu)
#endif
--
2.19.1