From: Yicong Yang <yangyicong@hisilicon.com> commit 4b455f59945aab5610828a1320b045c82cbe8852 upstream. Currently if architectures want to support HOTPLUG_SMT they need to provide a topology_is_primary_thread() telling the framework which thread in the SMT cannot offline. However arm64 doesn't have a restriction on which thread in the SMT cannot offline, a simplest choice is that just make 1st thread as the "primary" thread. So just make this as the default implementation in the framework and let architectures like x86 that have special primary thread to override this function (which they've already done). There's no need to provide a stub function if !CONFIG_SMP or !CONFIG_HOTPLUG_SMT. In such case the testing CPU is already the 1st CPU in the SMT so it's always the primary thread. Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com> Reviewed-by: Pierre Gondois <pierre.gondois@arm.com> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com> Reviewed-by: Yicong Yang <yangyicong@hisilicon.com> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com> Signed-off-by: Hongye Lin <linhongye@h-partners.com> Signed-off-by: Qi Xi <xiqi2@huawei.com> --- arch/x86/include/asm/topology.h | 1 - arch/x86/kernel/smpboot.c | 1 + include/linux/topology.h | 24 ++++++++++++++++++++++++ 3 files changed, 25 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h index 5b4f87329031..8bf8d5546e97 100644 --- a/arch/x86/include/asm/topology.h +++ b/arch/x86/include/asm/topology.h @@ -152,7 +152,6 @@ static inline int topology_phys_to_logical_die(unsigned int die, unsigned int cpu) { 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 diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 5726a3c9623e..2c897ad8b014 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -284,6 +284,7 @@ bool topology_is_primary_thread(unsigned int cpu) { return apic_id_is_primary_thread(per_cpu(x86_cpu_to_apicid, cpu)); } +#define topology_is_primary_thread topology_is_primary_thread /** * topology_smt_supported - Check whether SMT is supported by the CPUs diff --git a/include/linux/topology.h b/include/linux/topology.h index 80d27d717631..3aa7a3ef6771 100644 --- a/include/linux/topology.h +++ b/include/linux/topology.h @@ -212,6 +212,30 @@ static inline const struct cpumask *cpu_smt_mask(int cpu) } #endif +#ifndef topology_is_primary_thread + +#define topology_is_primary_thread topology_is_primary_thread + +static inline bool topology_is_primary_thread(unsigned int cpu) +{ + /* + * When disabling SMT the primary thread of the SMT will remain + * enabled/active. Architectures do have a special primary thread + * (e.g. x86) needs to override this function. Otherwise can make + * the first thread in the SMT as the primary thread. + * + * The sibling cpumask of an offline CPU contains always the CPU + * itself for architectures using the implementation of + * CONFIG_GENERIC_ARCH_TOPOLOGY for building their topology. + * Other architectures not using CONFIG_GENERIC_ARCH_TOPOLOGY for + * building their topology have to check whether to use this default + * implementation or to override it. + */ + return cpu == cpumask_first(topology_sibling_cpumask(cpu)); +} + +#endif + static inline const struct cpumask *cpu_cpu_mask(int cpu) { return cpumask_of_node(cpu_to_node(cpu)); -- 2.33.0