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authorMark Rutland <mark.rutland@arm.com>2016-11-03 23:23:11 +0300
committerCatalin Marinas <catalin.marinas@arm.com>2016-11-11 21:25:45 +0300
commit57c82954e77fa12c1023e87210d2ede77aaa0058 (patch)
treef038c648ae9e6352b1e7ba0590c2bea37cb56fc2
parent580efaa7ccfb8c0790dce4396434f0e5ac8d86ee (diff)
downloadlinux-57c82954e77fa12c1023e87210d2ede77aaa0058.tar.xz
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>
-rw-r--r--arch/arm64/include/asm/smp.h11
-rw-r--r--arch/arm64/kernel/smp.c5
2 files changed, 15 insertions, 1 deletions
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 <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;
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 <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;