On 2025/2/28 21:54, Sudeep Holla wrote: > On Tue, Feb 18, 2025 at 10:10:15PM +0800, Yicong Yang wrote: >> From: Yicong Yang <yangyic...@hisilicon.com> >> >> 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.came...@huawei.com> >> Signed-off-by: Yicong Yang <yangyic...@hisilicon.com> >> --- >> Pre questioned in v9 [1] whether this works on architectures not using >> CONFIG_GENERIC_ARCH_TOPOLOGY, See [2] for demonstration hacking on LoongArch >> VM and this also works. Architectures should use this on their own situation. >> [1] >> https://lore.kernel.org/linux-arm-kernel/427bd639-33c3-47e4-9e83-68c428eb1...@arm.com/ >> [2] >> https://lore.kernel.org/linux-arm-kernel/a5690fee-3019-f26c-8bad-1d95e388e...@huawei.com/ >> >> arch/powerpc/include/asm/topology.h | 1 + >> arch/x86/include/asm/topology.h | 2 +- >> include/linux/topology.h | 22 ++++++++++++++++++++++ >> 3 files changed, 24 insertions(+), 1 deletion(-) >> >> diff --git a/arch/powerpc/include/asm/topology.h >> b/arch/powerpc/include/asm/topology.h >> index 16bacfe8c7a2..da15b5efe807 100644 >> --- a/arch/powerpc/include/asm/topology.h >> +++ b/arch/powerpc/include/asm/topology.h >> @@ -152,6 +152,7 @@ static inline bool topology_is_primary_thread(unsigned >> int cpu) >> { >> return cpu == cpu_first_thread_sibling(cpu); >> } >> +#define topology_is_primary_thread topology_is_primary_thread >> >> static inline bool topology_smt_thread_allowed(unsigned int cpu) >> { >> diff --git a/arch/x86/include/asm/topology.h >> b/arch/x86/include/asm/topology.h >> index ec134b719144..6c79ee7c0957 100644 >> --- a/arch/x86/include/asm/topology.h >> +++ b/arch/x86/include/asm/topology.h >> @@ -229,11 +229,11 @@ static inline bool topology_is_primary_thread(unsigned >> int cpu) >> { >> return cpumask_test_cpu(cpu, cpu_primary_thread_mask); >> } >> +#define topology_is_primary_thread topology_is_primary_thread >> >> #else /* CONFIG_SMP */ >> static inline int topology_phys_to_logical_pkg(unsigned int pkg) { return >> 0; } >> static inline int topology_max_smt_threads(void) { return 1; } >> -static inline bool topology_is_primary_thread(unsigned int cpu) { return >> true; } >> static inline unsigned int topology_amd_nodes_per_pkg(void) { return 1; } >> #endif /* !CONFIG_SMP */ >> >> diff --git a/include/linux/topology.h b/include/linux/topology.h >> index 52f5850730b3..b3aba443c4eb 100644 >> --- a/include/linux/topology.h >> +++ b/include/linux/topology.h >> @@ -240,6 +240,28 @@ 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) >> +{ >> + /* >> + * On SMT hotplug the primary thread of the SMT won't be disabled. > > I may be misunderstanding the term "SMT hotplug" above. For me it is > comparable with logical CPU hotplug, so the above statement may be > misleading. IIUC, what you mean above is if SMT is disabled, the > primary thread will always remain enabled/active. Does that make sense > or am I missing something ? >
I just the borrow the term from kconfig HOTPLUG_SMT here, but here the statement only involves the disable part, so maybe it'll be more accurate to use "SMT disable" rather than "SMT hotplug" here? Thanks.
