From 57c82954e77fa12c1023e87210d2ede77aaa0058 Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Thu, 3 Nov 2016 20:23:11 +0000 Subject: [PATCH] arm64: make cpu number a percpu variable In the absence of CONFIG_THREAD_INFO_IN_TASK, core code maintains thread_info::cpu, and low-level architecture code can access this to build raw_smp_processor_id(). With CONFIG_THREAD_INFO_IN_TASK, core code maintains task_struct::cpu, which for reasons of hte header soup is not accessible to low-level arch code. Instead, we can maintain a percpu variable containing the cpu number. For both the old and new implementation of raw_smp_processor_id(), we read a syreg into a GPR, add an offset, and load the result. As the offset is now larger, it may not be folded into the load, but otherwise the assembly shouldn't change much. Signed-off-by: Mark Rutland Tested-by: Laura Abbott Cc: James Morse Cc: Suzuki K Poulose Cc: Will Deacon Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/smp.h | 11 ++++++++++- arch/arm64/kernel/smp.c | 5 +++++ 2 files changed, 15 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h index 022644704a93..968b08de820d 100644 --- a/arch/arm64/include/asm/smp.h +++ b/arch/arm64/include/asm/smp.h @@ -29,11 +29,20 @@ #ifndef __ASSEMBLY__ +#include + #include #include #include -#define raw_smp_processor_id() (current_thread_info()->cpu) +DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number); + +/* + * We don't use this_cpu_read(cpu_number) as that has implicit writes to + * preempt_count, and associated (compiler) barriers, that we'd like to avoid + * the expense of. If we're preemptible, the value can be stale at use anyway. + */ +#define raw_smp_processor_id() (*this_cpu_ptr(&cpu_number)) struct seq_file; diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index f64401faa091..6f42c68e457f 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -58,6 +58,9 @@ #define CREATE_TRACE_POINTS #include +DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number); +EXPORT_PER_CPU_SYMBOL(cpu_number); + /* * as from 2.5, kernels no longer have an init_tasks structure * so we need some other way of telling a new secondary core @@ -719,6 +722,8 @@ void __init smp_prepare_cpus(unsigned int max_cpus) */ for_each_possible_cpu(cpu) { + per_cpu(cpu_number, cpu) = cpu; + if (cpu == smp_processor_id()) continue;