arm64: make cpu number a percpu variable (57c82954) · Commits · 戴 / test

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>

arch/arm64/include/asm/smp.h

+10 −1

Original line number	Diff line number	Diff line
		@@ -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;

arch/arm64/kernel/smp.c

+5 −0

Original line number	Diff line number	Diff line
		@@ -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;

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