[BUG] Re: [PATCH 1/3] topology: Represent clusters of CPUs within a die

Jeremy Linton
2022-05-06T20:24:33Z

Hi,

It seems this set is:

"BUG: arch topology borken"
^code

on machines that don't actually have clusters, or provide a
representation which might be taken for a cluster. The Ampere Altra for
one. So, I guess its my job to relay what I was informed of when I
intially proposed something similar a few years back.

Neither the ACPI/PPTT spec nor the Arm architectural spec mandate the
concept of a "cluster" particularly in the form of a system with cores
sharing the L2, which IIRC is the case for the Kunpeng. And it tends to
be a shared L2 which gives the most bang for the buck (or was when I was
testing/benchmarking all this, on aarch64) from scheduler changes which
create cluster level scheduling domains. But OTOH, things like specJBB
didn't really like those smaller MC levels (which I suspect is hurt by
this change, without running a full benchmark suite, especially on
something like the above ampere, given what is happening to its
scheduling domains).

So, the one takeway I can give is this, the code below which is
attempting to create a cluster level should be a bit more intellegent
about whether there is an actual cluster. A first order approximation
might be adding a check to see if the node immediatly above the CPU
contains an L2 and that its shared. A better fix, of course is the
reason this wasn't previously done, and that is to convince the ACPI
commitee to standardize a CLUSTER level flag which could be utilized by
a firmware/machine manufactuer to decide whether cluster level
scheduling provides an advantage and simply not do it on machines which
don't flag CLUSTER levels because its not avantagious.

Thanks,

On 8/19/21 20:30, Barry Song wrote:
> 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 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>
> ---
> .../ABI/stable/sysfs-devices-system-cpu | 15 +++++
> Documentation/admin-guide/cputopology.rst | 12 ++--
> arch/arm64/kernel/topology.c | 2 +
> drivers/acpi/pptt.c | 67 +++++++++++++++++++
> 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 ++
> 9 files changed, 132 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/ABI/stable/sysfs-devices-system-cpu b/Documentation/ABI/stable/sysfs-devices-system-cpu
> index 516dafea03eb..3965ce504484 100644
> --- a/Documentation/ABI/stable/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/stable/sysfs-devices-system-cpu
> @@ -42,6 +42,12 @@ Description: the CPU core ID of cpuX. Typically it is the hardware platform's
> architecture and platform dependent.
> Values: integer
>
> +What: /sys/devices/system/cpu/cpuX/topology/cluster_id
> +Description: 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.
> +Values: integer
> +
> What: /sys/devices/system/cpu/cpuX/topology/book_id
> Description: the book ID of cpuX. Typically it is the hardware platform's
> identifier (rather than the kernel's). The actual value is
> @@ -85,6 +91,15 @@ Description: human-readable list of CPUs within the same die.
> The format is like 0-3, 8-11, 14,17.
> Values: decimal list.
>
> +What: /sys/devices/system/cpu/cpuX/topology/cluster_cpus
> +Description: internal kernel map of CPUs within the same cluster.
> +Values: hexadecimal bitmask.
> +
> +What: /sys/devices/system/cpu/cpuX/topology/cluster_cpus_list
> +Description: human-readable list of CPUs within the same cluster.
> + The format is like 0-3, 8-11, 14,17.
> +Values: decimal list.
> +
> What: /sys/devices/system/cpu/cpuX/topology/book_siblings
> Description: internal kernel map of cpuX's hardware threads within the same
> book_id. it's only used on s390.
> diff --git a/Documentation/admin-guide/cputopology.rst b/Documentation/admin-guide/cputopology.rst
> index 8632a1db36e4..a5491949880d 100644
> --- a/Documentation/admin-guide/cputopology.rst
> +++ b/Documentation/admin-guide/cputopology.rst
> @@ -19,11 +19,13 @@ 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)
> @@ -39,10 +41,12 @@ 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 4dd14a6620c1..9ab78ad826e2 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 fe69dc518f31..701f61c01359 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -746,6 +746,73 @@ 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;
> + 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
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 921312a8d957..5b1589adacaf 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -598,6 +598,11 @@ 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];
> @@ -615,6 +620,11 @@ 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);
>
> @@ -633,6 +643,9 @@ 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);
> @@ -648,6 +661,7 @@ void __init reset_cpu_topology(void)
>
> cpu_topo->thread_id = -1;
> cpu_topo->core_id = -1;
> + cpu_topo->cluster_id = -1;
> cpu_topo->package_id = -1;
> cpu_topo->llc_id = -1;
>
> diff --git a/drivers/base/topology.c b/drivers/base/topology.c
> index 43c0940643f5..8f2b641d0b8c 100644
> --- a/drivers/base/topology.c
> +++ b/drivers/base/topology.c
> @@ -48,6 +48,9 @@ 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);
>
> @@ -63,6 +66,10 @@ define_siblings_read_func(core_siblings, core_cpumask);
> static BIN_ATTR_RO(core_siblings, 0);
> static BIN_ATTR_RO(core_siblings_list, 0);
>
> +define_siblings_read_func(cluster_cpus, cluster_cpumask);
> +static BIN_ATTR_RO(cluster_cpus, 0);
> +static BIN_ATTR_RO(cluster_cpus_list, 0);
> +
> define_siblings_read_func(die_cpus, die_cpumask);
> static BIN_ATTR_RO(die_cpus, 0);
> static BIN_ATTR_RO(die_cpus_list, 0);
> @@ -94,6 +101,8 @@ static struct bin_attribute *bin_attrs[] = {
> &bin_attr_thread_siblings_list,
> &bin_attr_core_siblings,
> &bin_attr_core_siblings_list,
> + &bin_attr_cluster_cpus,
> + &bin_attr_cluster_cpus_list,
> &bin_attr_die_cpus,
> &bin_attr_die_cpus_list,
> &bin_attr_package_cpus,
> @@ -112,6 +121,7 @@ static struct bin_attribute *bin_attrs[] = {
> 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,
> #ifdef CONFIG_SCHED_BOOK
> &dev_attr_book_id.attr,
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 72e4f7fd268c..6d65427e5f67 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -1353,6 +1353,7 @@ 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);
> @@ -1365,6 +1366,10 @@ 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 f180240dc95f..b97cea83b25e 100644
> --- a/include/linux/arch_topology.h
> +++ b/include/linux/arch_topology.h
> @@ -62,10 +62,12 @@ 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;
> };
>
> @@ -73,13 +75,16 @@ 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 7634cd737061..80d27d717631 100644
> --- a/include/linux/topology.h
> +++ b/include/linux/topology.h
> @@ -186,6 +186,9 @@ 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
> @@ -195,6 +198,9 @@ 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