linux-kernel - Re: [patch 03/12] x86/irq/64: Adjust the per CPU irq stack pointer by 8

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Message-ID: <YB1NzV4Zxfmu7PEH@hirez.programming.kicks-ass.net>
Date:   Fri, 5 Feb 2021 14:53:17 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [patch 03/12] x86/irq/64: Adjust the per CPU irq stack pointer
 by 8

On Thu, Feb 04, 2021 at 09:49:06PM +0100, Thomas Gleixner wrote:
>  Move the definition
> next to the inuse flag so they end up in the same cache line.

> -DEFINE_PER_CPU(struct irq_stack *, hardirq_stack_ptr);
> +DEFINE_PER_CPU(void *, hardirq_stack_ptr);
>  DEFINE_PER_CPU(bool, hardirq_stack_inuse);

Not strictly guaranteed they end up in the same line. If you stick them
in a struct and force alignment on the instance you'll have better
guarantees.