Re: [PATCH] LoongArch: Add SMT (Simultaneous Multi-Threading) support

["Rafael J. Wysocki" <rafael@kernel.org>]

On Wed, Jun 14, 2023 at 11:38 AM Liupu Wang <wangliupu@loongson.cn> wrote:
>
> From: Huacai Chen <chenhuacai@loongson.cn>
>
> Loongson-3A6000 has SMT (Simultaneous Multi-Threading) support, each
> physical core has two logical cores (threads). This patch add SMT probe
> and scheduler support via ACPI PPTT.
>
> If SCHED_SMT enabled, Loongson-3A6000 is treated as 4 cores, 8 threads;
> If SCHED_SMT disabled, Loongson-3A6000 is treated as 8 cores, 8 threads.
>
> Remove smp_num_siblings to support HMP (Heterogeneous Multi-Processing).
>
> Signed-off-by: Liupu Wang <wangliupu@loongson.cn>
> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
> ---
>  arch/loongarch/Kconfig                |  8 +++++++
>  arch/loongarch/include/asm/acpi.h     |  9 ++++++++
>  arch/loongarch/include/asm/cpu-info.h |  1 +
>  arch/loongarch/kernel/acpi.c          | 32 +++++++++++++++++++++++++++
>  arch/loongarch/kernel/proc.c          |  1 +
>  arch/loongarch/kernel/smp.c           | 24 +++++++++-----------
>  drivers/acpi/Kconfig                  |  2 +-
>  7 files changed, 62 insertions(+), 15 deletions(-)
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index d38b066fc931..6d36b681068e 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -5,6 +5,7 @@ config LOONGARCH
>         select ACPI
>         select ACPI_GENERIC_GSI if ACPI
>         select ACPI_MCFG if ACPI
> +       select ACPI_PPTT if ACPI
>         select ACPI_SYSTEM_POWER_STATES_SUPPORT if ACPI
>         select ARCH_BINFMT_ELF_STATE
>         select ARCH_ENABLE_MEMORY_HOTPLUG
> @@ -372,6 +373,13 @@ config EFI_STUB
>           This kernel feature allows the kernel to be loaded directly by
>           EFI firmware without the use of a bootloader.
>
> +config SCHED_SMT
> +       bool "SMT scheduler support"
> +       default y
> +       help
> +         Improves scheduler's performance when there are multiple
> +         threads in one physical core.
> +
>  config SMP
>         bool "Multi-Processing support"
>         help
> diff --git a/arch/loongarch/include/asm/acpi.h b/arch/loongarch/include/asm/acpi.h
> index 976a810352c6..5c78b5d2bfb7 100644
> --- a/arch/loongarch/include/asm/acpi.h
> +++ b/arch/loongarch/include/asm/acpi.h
> @@ -13,6 +13,7 @@ extern int acpi_strict;
>  extern int acpi_disabled;
>  extern int acpi_pci_disabled;
>  extern int acpi_noirq;
> +extern int pptt_enabled;
>
>  #define acpi_os_ioremap acpi_os_ioremap
>  void __iomem *acpi_os_ioremap(acpi_physical_address phys, acpi_size size);
> @@ -30,6 +31,14 @@ static inline bool acpi_has_cpu_in_madt(void)
>  }
>
>  extern struct list_head acpi_wakeup_device_list;
> +extern struct acpi_madt_core_pic acpi_core_pic[NR_CPUS];
> +
> +extern int __init parse_acpi_topology(void);
> +
> +static inline u32 get_acpi_id_for_cpu(unsigned int cpu)
> +{
> +       return acpi_core_pic[cpu_logical_map(cpu)].processor_id;
> +}
>
>  #endif /* !CONFIG_ACPI */
>
> diff --git a/arch/loongarch/include/asm/cpu-info.h b/arch/loongarch/include/asm/cpu-info.h
> index cd73a6f57fe3..900589cb159d 100644
> --- a/arch/loongarch/include/asm/cpu-info.h
> +++ b/arch/loongarch/include/asm/cpu-info.h
> @@ -54,6 +54,7 @@ struct cpuinfo_loongarch {
>         struct cache_desc       cache_leaves[CACHE_LEAVES_MAX];
>         int                     core;   /* physical core number in package */
>         int                     package;/* physical package number */
> +       int                     global_id; /* physical global thread number */
>         int                     vabits; /* Virtual Address size in bits */
>         int                     pabits; /* Physical Address size in bits */
>         unsigned int            ksave_mask; /* Usable KSave mask. */
> diff --git a/arch/loongarch/kernel/acpi.c b/arch/loongarch/kernel/acpi.c
> index 98f431157e4c..9450e09073eb 100644
> --- a/arch/loongarch/kernel/acpi.c
> +++ b/arch/loongarch/kernel/acpi.c
> @@ -33,6 +33,8 @@ u64 acpi_saved_sp;
>
>  #define PREFIX                 "ACPI: "
>
> +struct acpi_madt_core_pic acpi_core_pic[NR_CPUS];
> +
>  void __init __iomem * __acpi_map_table(unsigned long phys, unsigned long size)
>  {
>
> @@ -99,6 +101,7 @@ acpi_parse_processor(union acpi_subtable_headers *header, const unsigned long en
>
>         acpi_table_print_madt_entry(&header->common);
>  #ifdef CONFIG_SMP
> +       acpi_core_pic[processor->core_id] = *processor;
>         set_processor_mask(processor->core_id, processor->flags);
>  #endif
>
> @@ -140,6 +143,35 @@ static void __init acpi_process_madt(void)
>         loongson_sysconf.nr_cpus = num_processors;
>  }
>
> +int pptt_enabled;
> +
> +int __init parse_acpi_topology(void)
> +{
> +       int cpu, topology_id;
> +
> +       for_each_possible_cpu(cpu) {
> +               topology_id = find_acpi_cpu_topology(cpu, 0);
> +               if (topology_id < 0) {
> +                       pr_warn("Invalid BIOS PPTT\n");
> +                       return -ENOENT;
> +               }
> +
> +               if (acpi_pptt_cpu_is_thread(cpu) <= 0)
> +                       cpu_data[cpu].core = topology_id;
> +               else {
> +                       topology_id = find_acpi_cpu_topology(cpu, 1);
> +                       if (topology_id < 0)
> +                               return -ENOENT;
> +
> +                       cpu_data[cpu].core = topology_id;
> +               }
> +       }
> +
> +       pptt_enabled = 1;
> +
> +       return 0;
> +}
> +
>  #ifndef CONFIG_SUSPEND
>  int (*acpi_suspend_lowlevel)(void);
>  #else
> diff --git a/arch/loongarch/kernel/proc.c b/arch/loongarch/kernel/proc.c
> index 0d82907b5404..d4b270630bb5 100644
> --- a/arch/loongarch/kernel/proc.c
> +++ b/arch/loongarch/kernel/proc.c
> @@ -49,6 +49,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
>         seq_printf(m, "processor\t\t: %ld\n", n);
>         seq_printf(m, "package\t\t\t: %d\n", cpu_data[n].package);
>         seq_printf(m, "core\t\t\t: %d\n", cpu_data[n].core);
> +       seq_printf(m, "global_id\t\t: %d\n", cpu_data[n].global_id);
>         seq_printf(m, "CPU Family\t\t: %s\n", __cpu_family[n]);
>         seq_printf(m, "Model Name\t\t: %s\n", __cpu_full_name[n]);
>         seq_printf(m, "CPU Revision\t\t: 0x%02x\n", version);
> diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
> index ed167e244cda..062f3fe8df60 100644
> --- a/arch/loongarch/kernel/smp.c
> +++ b/arch/loongarch/kernel/smp.c
> @@ -8,6 +8,7 @@
>   * Copyright (C) 2000, 2001 Silicon Graphics, Inc.
>   * Copyright (C) 2000, 2001, 2003 Broadcom Corporation
>   */
> +#include <linux/acpi.h>
>  #include <linux/cpu.h>
>  #include <linux/cpumask.h>
>  #include <linux/init.h>
> @@ -37,10 +38,6 @@ EXPORT_SYMBOL(__cpu_number_map);
>  int __cpu_logical_map[NR_CPUS];                /* Map logical to physical */
>  EXPORT_SYMBOL(__cpu_logical_map);
>
> -/* Number of threads (siblings) per CPU core */
> -int smp_num_siblings = 1;
> -EXPORT_SYMBOL(smp_num_siblings);
> -
>  /* Representing the threads (siblings) of each logical CPU */
>  cpumask_t cpu_sibling_map[NR_CPUS] __read_mostly;
>  EXPORT_SYMBOL(cpu_sibling_map);
> @@ -228,9 +225,12 @@ void __init loongson_prepare_cpus(unsigned int max_cpus)
>  {
>         int i = 0;
>
> +       parse_acpi_topology();
> +
>         for (i = 0; i < loongson_sysconf.nr_cpus; i++) {
>                 set_cpu_present(i, true);
>                 csr_mail_send(0, __cpu_logical_map[i], 0);
> +               cpu_data[i].global_id = __cpu_logical_map[i];
>         }
>
>         per_cpu(cpu_state, smp_processor_id()) = CPU_ONLINE;
> @@ -271,10 +271,10 @@ void loongson_init_secondary(void)
>         numa_add_cpu(cpu);
>  #endif
>         per_cpu(cpu_state, cpu) = CPU_ONLINE;
> -       cpu_data[cpu].core =
> -                    cpu_logical_map(cpu) % loongson_sysconf.cores_per_package;
>         cpu_data[cpu].package =
>                      cpu_logical_map(cpu) / loongson_sysconf.cores_per_package;
> +       cpu_data[cpu].core = pptt_enabled ? cpu_data[cpu].core :
> +                    cpu_logical_map(cpu) % loongson_sysconf.cores_per_package;
>  }
>
>  void loongson_smp_finish(void)
> @@ -380,14 +380,10 @@ static inline void set_cpu_sibling_map(int cpu)
>
>         cpumask_set_cpu(cpu, &cpu_sibling_setup_map);
>
> -       if (smp_num_siblings <= 1)
> -               cpumask_set_cpu(cpu, &cpu_sibling_map[cpu]);
> -       else {
> -               for_each_cpu(i, &cpu_sibling_setup_map) {
> -                       if (cpus_are_siblings(cpu, i)) {
> -                               cpumask_set_cpu(i, &cpu_sibling_map[cpu]);
> -                               cpumask_set_cpu(cpu, &cpu_sibling_map[i]);
> -                       }
> +       for_each_cpu(i, &cpu_sibling_setup_map) {
> +               if (cpus_are_siblings(cpu, i)) {
> +                       cpumask_set_cpu(i, &cpu_sibling_map[cpu]);
> +                       cpumask_set_cpu(cpu, &cpu_sibling_map[i]);
>                 }
>         }
>  }
> diff --git a/drivers/acpi/Kconfig b/drivers/acpi/Kconfig
> index ccbeab9500ec..00dd309b6682 100644
> --- a/drivers/acpi/Kconfig
> +++ b/drivers/acpi/Kconfig
> @@ -542,10 +542,10 @@ config ACPI_PFRUT
>
>  if ARM64
>  source "drivers/acpi/arm64/Kconfig"
> +endif
>
>  config ACPI_PPTT
>         bool
> -endif

x86 doesn't use PPTT as of today.  Why do you enable it for them?

>  config ACPI_PCC
>         bool "ACPI PCC Address Space"
> --