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

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Message-ID: <CAMzpN2iM_GdoPgQVu41k7dFGt4yy50K2pdzaRDQ=3STxyzp_Jg@mail.gmail.com>
Date: Wed, 26 Feb 2025 19:10:38 -0500
From: Brian Gerst <brgerst@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
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 3:25 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> 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?

I had it that way originally, but it wasn't packing efficiently before
I added SORT_BY_ALIGNMENT() to the linker script.  I'll change it
back.


Brian Gerst