From 3f9169196be55590a794b52f49637561ddd1ba4f Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Wed, 5 Jul 2023 16:51:35 +0200 Subject: cpu/SMT: Move SMT prototypes into cpu_smt.h In order to export the cpuhp_smt_control enum as part of the interface between generic and architecture code, the architecture code needs to include asm/topology.h. But that leads to circular header dependencies. So split the enum and related declarations into a separate header. [ ldufour: Reworded the commit's description ] Signed-off-by: Michael Ellerman Signed-off-by: Laurent Dufour Signed-off-by: Thomas Gleixner Tested-by: Zhang Rui Link: https://lore.kernel.org/r/20230705145143.40545-3-ldufour@linux.ibm.com --- arch/x86/include/asm/topology.h | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch') diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h index caf41c4869a0..ae49ed4417d0 100644 --- a/arch/x86/include/asm/topology.h +++ b/arch/x86/include/asm/topology.h @@ -136,6 +136,8 @@ static inline int topology_max_smt_threads(void) return __max_smt_threads; } +#include + int topology_update_package_map(unsigned int apicid, unsigned int cpu); int topology_update_die_map(unsigned int dieid, unsigned int cpu); int topology_phys_to_logical_pkg(unsigned int pkg); -- cgit v1.2.3 From 447ae4ac41130a7f127c2581a5e816bb0800b560 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Wed, 5 Jul 2023 16:51:37 +0200 Subject: cpu/SMT: Store the current/max number of threads Some architectures allow partial SMT states at boot time, ie. when not all SMT threads are brought online. To support that the SMT code needs to know the maximum number of SMT threads, and also the currently configured number. The architecture code knows the max number of threads, so have the architecture code pass that value to cpu_smt_set_num_threads(). Note that although topology_max_smt_threads() exists, it is not configured early enough to be used here. As architecture, like PowerPC, allows the threads number to be set through the kernel command line, also pass that value. [ ldufour: Slightly reword the commit message ] [ ldufour: Rename cpu_smt_check_topology and add a num_threads argument ] Signed-off-by: Michael Ellerman Signed-off-by: Laurent Dufour Signed-off-by: Thomas Gleixner Tested-by: Zhang Rui Link: https://lore.kernel.org/r/20230705145143.40545-5-ldufour@linux.ibm.com --- arch/x86/kernel/cpu/common.c | 2 +- include/linux/cpu_smt.h | 8 ++++++-- kernel/cpu.c | 21 ++++++++++++++++++++- 3 files changed, 27 insertions(+), 4 deletions(-) (limited to 'arch') diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 52683fddafaf..12a48a85da3d 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -2317,7 +2317,7 @@ void __init arch_cpu_finalize_init(void) * identify_boot_cpu() initialized SMT support information, let the * core code know. */ - cpu_smt_check_topology(); + cpu_smt_set_num_threads(smp_num_siblings, smp_num_siblings); if (!IS_ENABLED(CONFIG_SMP)) { pr_info("CPU: "); diff --git a/include/linux/cpu_smt.h b/include/linux/cpu_smt.h index 722c2e306fef..0c1664294b57 100644 --- a/include/linux/cpu_smt.h +++ b/include/linux/cpu_smt.h @@ -12,15 +12,19 @@ enum cpuhp_smt_control { #if defined(CONFIG_SMP) && defined(CONFIG_HOTPLUG_SMT) extern enum cpuhp_smt_control cpu_smt_control; +extern unsigned int cpu_smt_num_threads; extern void cpu_smt_disable(bool force); -extern void cpu_smt_check_topology(void); +extern void cpu_smt_set_num_threads(unsigned int num_threads, + unsigned int max_threads); extern bool cpu_smt_possible(void); extern int cpuhp_smt_enable(void); extern int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval); #else # define cpu_smt_control (CPU_SMT_NOT_IMPLEMENTED) +# define cpu_smt_num_threads 1 static inline void cpu_smt_disable(bool force) { } -static inline void cpu_smt_check_topology(void) { } +static inline void cpu_smt_set_num_threads(unsigned int num_threads, + unsigned int max_threads) { } static inline bool cpu_smt_possible(void) { return false; } static inline int cpuhp_smt_enable(void) { return 0; } static inline int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval) { return 0; } diff --git a/kernel/cpu.c b/kernel/cpu.c index b6fe170c93e9..d7dd535cb5b5 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -594,6 +594,8 @@ void __weak arch_smt_update(void) { } #ifdef CONFIG_HOTPLUG_SMT enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED; +static unsigned int cpu_smt_max_threads __ro_after_init; +unsigned int cpu_smt_num_threads __read_mostly = UINT_MAX; void __init cpu_smt_disable(bool force) { @@ -607,16 +609,33 @@ void __init cpu_smt_disable(bool force) pr_info("SMT: disabled\n"); cpu_smt_control = CPU_SMT_DISABLED; } + cpu_smt_num_threads = 1; } /* * The decision whether SMT is supported can only be done after the full * CPU identification. Called from architecture code. */ -void __init cpu_smt_check_topology(void) +void __init cpu_smt_set_num_threads(unsigned int num_threads, + unsigned int max_threads) { + WARN_ON(!num_threads || (num_threads > max_threads)); + if (!topology_smt_supported()) cpu_smt_control = CPU_SMT_NOT_SUPPORTED; + + cpu_smt_max_threads = max_threads; + + /* + * If SMT has been disabled via the kernel command line or SMT is + * not supported, set cpu_smt_num_threads to 1 for consistency. + * If enabled, take the architecture requested number of threads + * to bring up into account. + */ + if (cpu_smt_control != CPU_SMT_ENABLED) + cpu_smt_num_threads = 1; + else if (num_threads < cpu_smt_num_threads) + cpu_smt_num_threads = num_threads; } static int __init smt_cmdline_disable(char *str) -- cgit v1.2.3 From 91b4a7dbfe05ddb6fd3cf78cc11fb5ed64d3af90 Mon Sep 17 00:00:00 2001 From: Laurent Dufour Date: Wed, 5 Jul 2023 16:51:38 +0200 Subject: cpu/SMT: Remove topology_smt_supported() Since the maximum number of threads is now passed to cpu_smt_set_num_threads(), checking that value is enough to know whether SMT is supported. Suggested-by: Thomas Gleixner Signed-off-by: Laurent Dufour Signed-off-by: Thomas Gleixner Tested-by: Zhang Rui Link: https://lore.kernel.org/r/20230705145143.40545-6-ldufour@linux.ibm.com --- arch/x86/include/asm/topology.h | 2 -- arch/x86/kernel/smpboot.c | 8 -------- kernel/cpu.c | 4 ++-- 3 files changed, 2 insertions(+), 12 deletions(-) (limited to 'arch') diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h index ae49ed4417d0..3235ba1e5b06 100644 --- a/arch/x86/include/asm/topology.h +++ b/arch/x86/include/asm/topology.h @@ -141,7 +141,6 @@ static inline int topology_max_smt_threads(void) int topology_update_package_map(unsigned int apicid, unsigned int cpu); int topology_update_die_map(unsigned int dieid, unsigned int cpu); int topology_phys_to_logical_pkg(unsigned int pkg); -bool topology_smt_supported(void); extern struct cpumask __cpu_primary_thread_mask; #define cpu_primary_thread_mask ((const struct cpumask *)&__cpu_primary_thread_mask) @@ -164,7 +163,6 @@ static inline int topology_phys_to_logical_pkg(unsigned int pkg) { return 0; } static inline int topology_max_die_per_package(void) { return 1; } static inline int topology_max_smt_threads(void) { return 1; } static inline bool topology_is_primary_thread(unsigned int cpu) { return true; } -static inline bool topology_smt_supported(void) { return false; } #endif /* !CONFIG_SMP */ static inline void arch_fix_phys_package_id(int num, u32 slot) diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index e1aa2cd7734b..d4e897b820c4 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -326,14 +326,6 @@ static void notrace start_secondary(void *unused) cpu_startup_entry(CPUHP_AP_ONLINE_IDLE); } -/** - * topology_smt_supported - Check whether SMT is supported by the CPUs - */ -bool topology_smt_supported(void) -{ - return smp_num_siblings > 1; -} - /** * topology_phys_to_logical_pkg - Map a physical package id to a logical * @phys_pkg: The physical package id to map diff --git a/kernel/cpu.c b/kernel/cpu.c index d7dd535cb5b5..70add058e77b 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -621,7 +621,7 @@ void __init cpu_smt_set_num_threads(unsigned int num_threads, { WARN_ON(!num_threads || (num_threads > max_threads)); - if (!topology_smt_supported()) + if (max_threads == 1) cpu_smt_control = CPU_SMT_NOT_SUPPORTED; cpu_smt_max_threads = max_threads; @@ -1801,7 +1801,7 @@ early_param("cpuhp.parallel", parallel_bringup_parse_param); static inline bool cpuhp_smt_aware(void) { - return topology_smt_supported(); + return cpu_smt_max_threads > 1; } static inline const struct cpumask *cpuhp_get_primary_thread_mask(void) -- cgit v1.2.3 From 38253464bc821d6de6bba81bb1412ebb36f6cbd1 Mon Sep 17 00:00:00 2001 From: Michael Ellerman Date: Wed, 5 Jul 2023 16:51:39 +0200 Subject: cpu/SMT: Create topology_smt_thread_allowed() Some architectures allows partial SMT states, i.e. when not all SMT threads are brought online. To support that, add an architecture helper which checks whether a given CPU is allowed to be brought online depending on how many SMT threads are currently enabled. Since this is only applicable to architecture supporting partial SMT, only these architectures should select the new configuration variable CONFIG_SMT_NUM_THREADS_DYNAMIC. For the other architectures, not supporting the partial SMT states, there is no need to define topology_cpu_smt_allowed(), the generic code assumed that all the threads are allowed or only the primary ones. Call the helper from cpu_smt_enable(), and cpu_smt_allowed() when SMT is enabled, to check if the particular thread should be onlined. Notably, also call it from cpu_smt_disable() if CPU_SMT_ENABLED, to allow offlining some threads to move from a higher to lower number of threads online. [ ldufour: Slightly reword the commit's description ] [ ldufour: Introduce CONFIG_SMT_NUM_THREADS_DYNAMIC ] Suggested-by: Thomas Gleixner Signed-off-by: Michael Ellerman Signed-off-by: Laurent Dufour Signed-off-by: Thomas Gleixner Tested-by: Zhang Rui Link: https://lore.kernel.org/r/20230705145143.40545-7-ldufour@linux.ibm.com --- arch/Kconfig | 3 +++ kernel/cpu.c | 24 +++++++++++++++++++++++- 2 files changed, 26 insertions(+), 1 deletion(-) (limited to 'arch') diff --git a/arch/Kconfig b/arch/Kconfig index aff2746c8af2..63c5d6a2022b 100644 --- a/arch/Kconfig +++ b/arch/Kconfig @@ -34,6 +34,9 @@ config ARCH_HAS_SUBPAGE_FAULTS config HOTPLUG_SMT bool +config SMT_NUM_THREADS_DYNAMIC + bool + # Selected by HOTPLUG_CORE_SYNC_DEAD or HOTPLUG_CORE_SYNC_FULL config HOTPLUG_CORE_SYNC bool diff --git a/kernel/cpu.c b/kernel/cpu.c index 70add058e77b..9a8d0685e055 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -645,9 +645,23 @@ static int __init smt_cmdline_disable(char *str) } early_param("nosmt", smt_cmdline_disable); +/* + * For Archicture supporting partial SMT states check if the thread is allowed. + * Otherwise this has already been checked through cpu_smt_max_threads when + * setting the SMT level. + */ +static inline bool cpu_smt_thread_allowed(unsigned int cpu) +{ +#ifdef CONFIG_SMT_NUM_THREADS_DYNAMIC + return topology_smt_thread_allowed(cpu); +#else + return true; +#endif +} + static inline bool cpu_smt_allowed(unsigned int cpu) { - if (cpu_smt_control == CPU_SMT_ENABLED) + if (cpu_smt_control == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu)) return true; if (topology_is_primary_thread(cpu)) @@ -2642,6 +2656,12 @@ int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval) for_each_online_cpu(cpu) { if (topology_is_primary_thread(cpu)) continue; + /* + * Disable can be called with CPU_SMT_ENABLED when changing + * from a higher to lower number of SMT threads per core. + */ + if (ctrlval == CPU_SMT_ENABLED && cpu_smt_thread_allowed(cpu)) + continue; ret = cpu_down_maps_locked(cpu, CPUHP_OFFLINE); if (ret) break; @@ -2676,6 +2696,8 @@ int cpuhp_smt_enable(void) /* Skip online CPUs and CPUs on offline nodes */ if (cpu_online(cpu) || !node_online(cpu_to_node(cpu))) continue; + if (!cpu_smt_thread_allowed(cpu)) + continue; ret = _cpu_up(cpu, 0, CPUHP_ONLINE); if (ret) break; -- cgit v1.2.3