Commit f7f69dfb authored Nov 03, 2016 by Mark Rutland Committed by Zubin Mithra Aug 09, 2017

UPSTREAM: 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 <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>

Bug: 38331309
Change-Id: I154927b0f9fc0ebbbed88c9958408bbb19cf09de
(cherry picked from commit 57c82954e77fa12c1023e87210d2ede77aaa0058)
Signed-off-by: Zubin Mithra <zsm@google.com>

parent d8cd9de3

arch/arm64/include/asm/smp.h

+10 −1

Original line number	Diff line number	Diff line
		@@ -16,11 +16,20 @@
		#ifndef __ASM_SMP_H
		#define __ASM_SMP_H

		#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
		@@ -57,6 +57,9 @@
		#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
		@@ -608,6 +611,8 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
		if (max_cpus == 0)
		break;

		per_cpu(cpu_number, cpu) = cpu;

		if (cpu == smp_processor_id())
		continue;