linux-kernel - Re: [PATCH v2 07/11] x86/irq: Move irq stacks to percpu hot section

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Message-ID: <20250226202554.GC29387@noisy.programming.kicks-ass.net>
Date: Wed, 26 Feb 2025 21:25:54 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Brian Gerst <brgerst@...il.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
	Ingo Molnar <mingo@...nel.org>, "H . Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>, Ard Biesheuvel <ardb@...nel.org>,
	Uros Bizjak <ubizjak@...il.com>,
	Linus Torvalds <torvalds@...uxfoundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2 07/11] x86/irq: Move irq stacks to percpu hot section

On Wed, Feb 26, 2025 at 01:05:26PM -0500, Brian Gerst wrote:

> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
> index 474af15ae017..2cd2064457b1 100644
> --- a/arch/x86/kernel/irq.c
> +++ b/arch/x86/kernel/irq.c
> @@ -34,6 +34,11 @@ EXPORT_PER_CPU_SYMBOL(irq_stat);
>  DEFINE_PER_CPU_CACHE_HOT(u16, __softirq_pending);
>  EXPORT_PER_CPU_SYMBOL(__softirq_pending);
>  
> +DEFINE_PER_CPU_CACHE_HOT(struct irq_stack *, hardirq_stack_ptr);
> +#ifdef CONFIG_X86_64
> +DEFINE_PER_CPU_CACHE_HOT(bool, hardirq_stack_inuse);
> +#endif
> +
>  atomic_t irq_err_count;
>  
>  /*

Perhaps instead of the above #ifdef,...

> diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
> index dc1049c01f9b..48a27cde9635 100644
> --- a/arch/x86/kernel/irq_32.c
> +++ b/arch/x86/kernel/irq_32.c
> @@ -52,6 +52,8 @@ static inline int check_stack_overflow(void) { return 0; }
>  static inline void print_stack_overflow(void) { }
>  #endif
>  
> +DEFINE_PER_CPU_CACHE_HOT(struct irq_stack *, softirq_stack_ptr);
> +
>  static void call_on_stack(void *func, void *stack)
>  {
>  	asm volatile("xchgl	%%ebx,%%esp	\n"

> diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
> index 56bdeecd8ee0..4834e317e568 100644
> --- a/arch/x86/kernel/irq_64.c
> +++ b/arch/x86/kernel/irq_64.c

stick it in this file, like you already did for the 32bit case?