[Linuxarm] Re: [RFC PATCH v4 1/3] topology: Represent clusters of CPUs within a die.

On Mon, 15 Mar 2021 03:11:06 +0000 "Song Bao Hua (Barry Song)" song.bao.hua@hisilicon.com wrote:

...

-----Original Message----- From: Song Bao Hua (Barry Song) Sent: Tuesday, March 2, 2021 12:00 PM To: tim.c.chen@linux.intel.com; catalin.marinas@arm.com; will@kernel.org; rjw@rjwysocki.net; vincent.guittot@linaro.org; bp@alien8.de; tglx@linutronix.de; mingo@redhat.com; lenb@kernel.org; peterz@infradead.org; dietmar.eggemann@arm.com; rostedt@goodmis.org; bsegall@google.com; mgorman@suse.de Cc: msys.mizuma@gmail.com; valentin.schneider@arm.com; gregkh@linuxfoundation.org; Jonathan Cameron jonathan.cameron@huawei.com; juri.lelli@redhat.com; mark.rutland@arm.com; sudeep.holla@arm.com; aubrey.li@linux.intel.com; linux-arm-kernel@lists.infradead.org; linux-kernel@vger.kernel.org; linux-acpi@vger.kernel.org; x86@kernel.org; xuwei (O) xuwei5@huawei.com; Zengtao (B) prime.zeng@hisilicon.com; guodong.xu@linaro.org; yangyicong yangyicong@huawei.com; Liguozhu (Kenneth) liguozhu@hisilicon.com; linuxarm@openeuler.org; hpa@zytor.com; Jonathan Cameron jonathan.cameron@huawei.com; Song Bao Hua (Barry Song) song.bao.hua@hisilicon.com Subject: [RFC PATCH v4 1/3] topology: Represent clusters of CPUs within a die.

From: Jonathan Cameron Jonathan.Cameron@huawei.com

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 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 tell the scheduler to use the cache affinity of the cluster to make better decision on thread migration.

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.

[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: Barry Song song.bao.hua@hisilicon.com

---

-v4:

• used acpi_cpu_id for acpi_find_processor_node(addressing Masa's comment)

Documentation/admin-guide/cputopology.rst | 26 +++++++++++-- arch/arm64/kernel/topology.c | 2 + drivers/acpi/pptt.c | 63 +++++++++++++++++++++++++++++++ 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, 127 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/cputopology.rst b/Documentation/admin-guide/cputopology.rst index b90dafc..f9d3745 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 f6faa69..fe076b3 100644 --- a/arch/arm64/kernel/topology.c +++ b/arch/arm64/kernel/topology.c @@ -103,6 +103,8 @@ 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 4ae9335..11f8b02 100644 --- a/drivers/acpi/pptt.c +++ b/drivers/acpi/pptt.c @@ -737,6 +737,69 @@ 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;
  

• }
  

• }
• 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 de8587c..3079232 100644 --- a/drivers/base/arch_topology.c +++ b/drivers/base/arch_topology.c @@ -506,6 +506,11 @@ 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]; @@ -523,6 +528,11 @@ 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);
  

• }
  

I am seeing a machine without cluster is getting cluster, so I guess we need the below:

Makes sense and is inline with the docs above.

Thanks,

Jonathan

diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c index 3079232ed8ed..ccd4b3b5cc6f 100644 --- a/drivers/base/arch_topology.c +++ b/drivers/base/arch_topology.c @@ -528,7 +528,8 @@ 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) {
  

•           if (cpuid_topo->cluster_id == cpu_topo->cluster_id &&
  

•               cpu_topo->cluster_id != -1) {
                    cpumask_set_cpu(cpu, &cpuid_topo->cluster_sibling);
                    cpumask_set_cpu(cpuid, &cpu_topo->cluster_sibling);
            }
  

@@ -568,6 +569,7 @@ void __init reset_cpu_topology(void) struct cpu_topology *cpu_topo = &cpu_topology[cpu];

            cpu_topo->thread_id = -1;

•           cpu_topo->cluster_id = -1;
            cpu_topo->core_id = -1;
            cpu_topo->package_id = -1;
            cpu_topo->llc_id = -1;
  
  

Hi Jonathan, thoughts?

Thanks Barry