From mboxrd@z Thu Jan 1 00:00:00 1970 From: mark.rutland@arm.com (Mark Rutland) Date: Wed, 19 Oct 2016 20:10:32 +0100 Subject: [PATCH 08/10] arm64: make cpu number a percpu variable In-Reply-To: <1476904234-9511-1-git-send-email-mark.rutland@arm.com> References: <1476904234-9511-1-git-send-email-mark.rutland@arm.com> Message-ID: <1476904234-9511-9-git-send-email-mark.rutland@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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. Non-preemptible code will receive the current CPU's number, while preemptible code may race (as was previosuly the case), and see a stale value. Thus, there shouldn't be a change in observable behaviour. 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 large, it probably won't be folded into the load, but otherwise the assembly shouldn't change much. Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: James Morse Cc: Suzuki K Poulose Cc: Will Deacon --- arch/arm64/include/asm/smp.h | 6 +++++- arch/arm64/kernel/smp.c | 5 +++++ 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/smp.h b/arch/arm64/include/asm/smp.h index 0226447..f77ac0d 100644 --- a/arch/arm64/include/asm/smp.h +++ b/arch/arm64/include/asm/smp.h @@ -29,11 +29,15 @@ #ifndef __ASSEMBLY__ +#include + #include #include #include -#define raw_smp_processor_id() (current_thread_info()->cpu) +DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number); + +#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 7af46bf..2679722 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 @@ -718,6 +721,8 @@ 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; -- 1.9.1