linux-kernel - Re: [PATCH 3/8] arm64: Extend support for CONFIG_FUNCTION

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Message-ID: <20230110204320.GA9739@willie-the-truck>
Date:   Tue, 10 Jan 2023 20:43:20 +0000
From:   Will Deacon <will@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
        lenb@...nel.org, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, mhiramat@...nel.org,
        ndesaulniers@...gle.com, ojeda@...nel.org,
        rafael.j.wysocki@...el.com, revest@...omium.org,
        robert.moore@...el.com, rostedt@...dmis.org
Subject: Re: [PATCH 3/8] arm64: Extend support for CONFIG_FUNCTION_ALIGNMENT

On Tue, Jan 10, 2023 at 09:35:18PM +0100, Peter Zijlstra wrote:
> On Mon, Jan 09, 2023 at 01:58:23PM +0000, Mark Rutland wrote:
> 
> > diff --git a/arch/arm64/include/asm/linkage.h b/arch/arm64/include/asm/linkage.h
> > index 1436fa1cde24d..df18a3446ce82 100644
> > --- a/arch/arm64/include/asm/linkage.h
> > +++ b/arch/arm64/include/asm/linkage.h
> > @@ -5,8 +5,14 @@
> >  #include <asm/assembler.h>
> >  #endif
> >  
> > -#define __ALIGN		.align 2
> > -#define __ALIGN_STR	".align 2"
> > +#if CONFIG_FUNCTION_ALIGNMENT > 0
> > +#define ARM64_FUNCTION_ALIGNMENT	CONFIG_FUNCTION_ALIGNMENT
> > +#else
> > +#define ARM64_FUNCTION_ALIGNMENT	4
> > +#endif
> > +
> > +#define __ALIGN		.balign ARM64_FUNCTION_ALIGNMENT
> > +#define __ALIGN_STR	".balign " #ARM64_FUNCTION_ALIGNMENT
> 
> Isn't that much the same as having ARM64 select FUNCTION_ALIGNMENT_4B
> and simply removing all these lines and relying on the default
> behaviour?

There's a proposal (with some rough performance claims) to select
FUNCTION_ALIGNMENT_16B over at:

https://lore.kernel.org/r/20221208053649.540891-1-almasrymina@google.com

so we could just go with that?

Will