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arm64: make cpu number a percpu variable

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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 <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Cc: James Morse <james.morse@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Mark Rutland 2016-11-03 20:23:11 +00:00 committed by Catalin Marinas
parent 580efaa7cc
commit 57c82954e7
2 changed files with 15 additions and 1 deletions
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11
arch/arm64/include/asm/smp.h
View File

@ -29,11 +29,20 @@
#ifndef __ASSEMBLY__
#include <asm/percpu.h>
#include <linux/threads.h>
#include <linux/cpumask.h>
#include <linux/thread_info.h>
#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;

5
arch/arm64/kernel/smp.c
View File

@ -58,6 +58,9 @@
#define CREATE_TRACE_POINTS
#include <trace/events/ipi.h>
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;