x86/mm: Tidy up "x86/mm: Flush more aggressively in lazy TLB mode" (4e57b946) · Commits · 戴 / test

arch/x86/include/asm/tlbflush.h

+6 −1

Original line number	Diff line number	Diff line
		@@ -87,7 +87,12 @@ static inline u64 inc_mm_tlb_gen(struct mm_struct *mm)
		* to init_mm when we switch to a kernel thread (e.g. the idle thread). If
		* it's false, then we immediately switch CR3 when entering a kernel thread.
		*/
		DECLARE_STATIC_KEY_TRUE(tlb_use_lazy_mode);
		DECLARE_STATIC_KEY_TRUE(__tlb_defer_switch_to_init_mm);

		static inline bool tlb_defer_switch_to_init_mm(void)
		{
		return static_branch_unlikely(&__tlb_defer_switch_to_init_mm);
		}

		/*
		* 6 because 6 should be plenty and struct tlb_state will fit in

arch/x86/mm/tlb.c

+18 −12

Original line number	Diff line number	Diff line
		@@ -30,7 +30,7 @@

		atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1);

		DEFINE_STATIC_KEY_TRUE(tlb_use_lazy_mode);
		DEFINE_STATIC_KEY_TRUE(__tlb_defer_switch_to_init_mm);

		static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen,
		u16 new_asid, bool need_flush)
		@@ -213,6 +213,9 @@ void switch_mm_irqs_off(struct mm_struct prev, struct mm_struct next,
		}

		/*
		* Please ignore the name of this function. It should be called
		* switch_to_kernel_thread().
		*
		* enter_lazy_tlb() is a hint from the scheduler that we are entering a
		* kernel thread or other context without an mm. Acceptable implementations
		* include doing nothing whatsoever, switching to init_mm, or various clever
		@@ -227,7 +230,7 @@ void enter_lazy_tlb(struct mm_struct mm, struct task_struct tsk)
		if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm)
		return;

		if (static_branch_unlikely(&tlb_use_lazy_mode)) {
		if (tlb_defer_switch_to_init_mm()) {
		/*
		* There's a significant optimization that may be possible
		* here. We have accurate enough TLB flush tracking that we
		@@ -632,7 +635,8 @@ static ssize_t tlblazy_read_file(struct file file, char __user user_buf,
		{
		char buf[2];

		buf[0] = static_branch_likely(&tlb_use_lazy_mode) ? '1' : '0';
		buf[0] = static_branch_likely(&__tlb_defer_switch_to_init_mm)
		? '1' : '0';
		buf[1] = '\n';

		return simple_read_from_buffer(user_buf, count, ppos, buf, 2);
		@@ -647,9 +651,9 @@ static ssize_t tlblazy_write_file(struct file *file,
		return -EINVAL;

		if (val)
		static_branch_enable(&tlb_use_lazy_mode);
		static_branch_enable(&__tlb_defer_switch_to_init_mm);
		else
		static_branch_disable(&tlb_use_lazy_mode);
		static_branch_disable(&__tlb_defer_switch_to_init_mm);

		return count;
		}
		@@ -660,23 +664,25 @@ static const struct file_operations fops_tlblazy = {
		.llseek = default_llseek,
		};

		static int __init init_tlb_use_lazy_mode(void)
		static int __init init_tlblazy(void)
		{
		if (boot_cpu_has(X86_FEATURE_PCID)) {
		/*
		* Heuristic: with PCID on, switching to and from
		* init_mm is reasonably fast, but remote flush IPIs
		* as expensive as ever, so turn off lazy TLB mode.
		* If we have PCID, then switching to init_mm is reasonably
		* fast. If we don't have PCID, then switching to init_mm is
		* quite slow, so we default to trying to defer it in the
		* hopes that we can avoid it entirely. The latter approach
		* runs the risk of receiving otherwise unnecessary IPIs.
		*
		* We can't do this in setup_pcid() because static keys
		* haven't been initialized yet, and it would blow up
		* badly.
		*/
		static_branch_disable(&tlb_use_lazy_mode);
		static_branch_disable(&__tlb_defer_switch_to_init_mm);
		}

		debugfs_create_file("tlb_use_lazy_mode", S_IRUSR \| S_IWUSR,
		debugfs_create_file("tlb_defer_switch_to_init_mm", S_IRUSR \| S_IWUSR,
		arch_debugfs_dir, NULL, &fops_tlblazy);
		return 0;
		}
		late_initcall(init_tlb_use_lazy_mode);
		late_initcall(init_tlblazy);

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