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x86, percpu: Collect hot percpu variables into one cacheline
On x86_64, percpu variables current_task and kernel_stack are used for get_current() and current_thread_info() respectively and thus are often used close to each other. Move definition of current_task to kernel/cpu/common.c right above kernel_stack definition and align it to cacheline so that they always fall into the same cacheline. Two percpu variables defined there together - irq_stack_ptr and irq_count - are also pretty hot and will benefit from sharing the cacheline. For consistency, current_task definition for x86_32 is also moved to kernel/cpu/common.c. Putting current_task and kernel_stack into the same cacheline was suggested by Linus Torvalds. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: H. Peter Anvin <hpa@zytor.com>
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arch/x86/kernel
@ -987,13 +987,21 @@ struct desc_ptr idt_descr = { 256 * 16 - 1, (unsigned long) idt_table };
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DEFINE_PER_CPU_FIRST(union irq_stack_union,
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irq_stack_union) __aligned(PAGE_SIZE);
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DEFINE_PER_CPU(char *, irq_stack_ptr) =
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init_per_cpu_var(irq_stack_union.irq_stack) + IRQ_STACK_SIZE - 64;
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/*
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* The following four percpu variables are hot. Align current_task to
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* cacheline size such that all four fall in the same cacheline.
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*/
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DEFINE_PER_CPU(struct task_struct *, current_task) ____cacheline_aligned =
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&init_task;
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EXPORT_PER_CPU_SYMBOL(current_task);
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DEFINE_PER_CPU(unsigned long, kernel_stack) =
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(unsigned long)&init_thread_union - KERNEL_STACK_OFFSET + THREAD_SIZE;
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EXPORT_PER_CPU_SYMBOL(kernel_stack);
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DEFINE_PER_CPU(char *, irq_stack_ptr) =
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init_per_cpu_var(irq_stack_union.irq_stack) + IRQ_STACK_SIZE - 64;
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DEFINE_PER_CPU(unsigned int, irq_count) = -1;
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/*
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@ -1041,6 +1049,9 @@ DEFINE_PER_CPU(struct orig_ist, orig_ist);
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#else /* CONFIG_X86_64 */
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DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
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EXPORT_PER_CPU_SYMBOL(current_task);
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#ifdef CONFIG_CC_STACKPROTECTOR
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DEFINE_PER_CPU(unsigned long, stack_canary);
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#endif
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@ -61,9 +61,6 @@
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asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
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DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
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EXPORT_PER_CPU_SYMBOL(current_task);
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/*
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* Return saved PC of a blocked thread.
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*/
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@ -55,9 +55,6 @@
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asmlinkage extern void ret_from_fork(void);
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DEFINE_PER_CPU(struct task_struct *, current_task) = &init_task;
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EXPORT_PER_CPU_SYMBOL(current_task);
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DEFINE_PER_CPU(unsigned long, old_rsp);
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static DEFINE_PER_CPU(unsigned char, is_idle);
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