The following commit has been merged into the x86/core branch of tip: Commit-ID: e57ef2ed97c1d078973298658a8096644a1e9e09 Gitweb: https://git.kernel.org/tip/e57ef2ed97c1d078973298658a8096644a1e9e09 Author: Thomas Gleixner <tglx@xxxxxxxxxxxxx> AuthorDate: Thu, 15 Sep 2022 13:11:01 +02:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Mon, 17 Oct 2022 16:41:03 +02:00 x86: Put hot per CPU variables into a struct 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@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20220915111145.179707194@xxxxxxxxxxxxx --- arch/x86/include/asm/current.h | 19 ++++++++++++++++--- arch/x86/kernel/cpu/common.c | 14 +++++--------- arch/x86/kernel/process_32.c | 2 +- arch/x86/kernel/process_64.c | 2 +- arch/x86/kernel/smpboot.c | 2 +- 5 files changed, 24 insertions(+), 15 deletions(-) diff --git a/arch/x86/include/asm/current.h b/arch/x86/include/asm/current.h index 3e204e6..63c42ac 100644 --- a/arch/x86/include/asm/current.h +++ b/arch/x86/include/asm/current.h @@ -3,16 +3,29 @@ #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() diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c index 8e87318..5207153 100644 --- a/arch/x86/kernel/cpu/common.c +++ b/arch/x86/kernel/cpu/common.c @@ -2012,18 +2012,16 @@ static __init int setup_clearcpuid(char *arg) } __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); @@ -2083,8 +2081,6 @@ void syscall_init(void) #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); diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c index 2f314b1..807da45 100644 --- a/arch/x86/kernel/process_32.c +++ b/arch/x86/kernel/process_32.c @@ -207,7 +207,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) 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(); diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c index 6b3418b..c4f6cac 100644 --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -617,7 +617,7 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p) /* * 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(); diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index ce8728d..05f3157 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -1046,7 +1046,7 @@ int common_cpu_up(unsigned int cpu, struct task_struct *idle) /* 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) */
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