The layout of per-cpu variables is at the mercy of the compiler. This
can lead to random performance fluctuations from build to build.
Create a structure to hold some of the hottest per-cpu variables,
starting with current_task.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111145.179707194@infradead.org
#define _ASM_X86_CURRENT_H
#include <linux/compiler.h>
-#include <asm/percpu.h>
#ifndef __ASSEMBLY__
+
+#include <linux/cache.h>
+#include <asm/percpu.h>
+
struct task_struct;
-DECLARE_PER_CPU(struct task_struct *, current_task);
+struct pcpu_hot {
+ union {
+ struct {
+ struct task_struct *current_task;
+ };
+ u8 pad[64];
+ };
+};
+static_assert(sizeof(struct pcpu_hot) == 64);
+
+DECLARE_PER_CPU_ALIGNED(struct pcpu_hot, pcpu_hot);
static __always_inline struct task_struct *get_current(void)
{
- return this_cpu_read_stable(current_task);
+ return this_cpu_read_stable(pcpu_hot.current_task);
}
#define current get_current()
}
__setup("clearcpuid=", setup_clearcpuid);
+DEFINE_PER_CPU_ALIGNED(struct pcpu_hot, pcpu_hot) = {
+ .current_task = &init_task,
+};
+EXPORT_PER_CPU_SYMBOL(pcpu_hot);
+
#ifdef CONFIG_X86_64
DEFINE_PER_CPU_FIRST(struct fixed_percpu_data,
fixed_percpu_data) __aligned(PAGE_SIZE) __visible;
EXPORT_PER_CPU_SYMBOL_GPL(fixed_percpu_data);
-/*
- * The following percpu variables are hot. Align current_task to
- * cacheline size such that they fall in the same cacheline.
- */
-DEFINE_PER_CPU(struct task_struct *, current_task) ____cacheline_aligned =
- &init_task;
-EXPORT_PER_CPU_SYMBOL(current_task);
DEFINE_PER_CPU(void *, hardirq_stack_ptr);
DEFINE_PER_CPU(bool, hardirq_stack_inuse);
#else /* CONFIG_X86_64 */
-DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
-EXPORT_PER_CPU_SYMBOL(current_task);
DEFINE_PER_CPU(int, __preempt_count) = INIT_PREEMPT_COUNT;
EXPORT_PER_CPU_SYMBOL(__preempt_count);
if (prev->gs | next->gs)
loadsegment(gs, next->gs);
- this_cpu_write(current_task, next_p);
+ raw_cpu_write(pcpu_hot.current_task, next_p);
switch_fpu_finish();
/*
* Switch the PDA and FPU contexts.
*/
- this_cpu_write(current_task, next_p);
+ raw_cpu_write(pcpu_hot.current_task, next_p);
this_cpu_write(cpu_current_top_of_stack, task_top_of_stack(next_p));
switch_fpu_finish();
/* Just in case we booted with a single CPU. */
alternatives_enable_smp();
- per_cpu(current_task, cpu) = idle;
+ per_cpu(pcpu_hot.current_task, cpu) = idle;
cpu_init_stack_canary(cpu, idle);
/* Initialize the interrupt stack(s) */