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

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Message-ID: <87tuqq8sr3.fsf@nanos.tec.linutronix.de>
Date:   Fri, 05 Feb 2021 16:00:00 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Peter Zijlstra <peterz@...radead.org>
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 Fri, Feb 05 2021 at 14:53, Peter Zijlstra wrote:
> 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.

You're right. There are a bunch of per cpu variables which are randomly
defined all over the place which should stay in the same cache line.