linux-kernel - Re: [PATCH] um/asm: Replace "REP; NOP" with PAUSE mnemonic

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Message-ID: <20250415185558.112621df@pumpkin>
Date: Tue, 15 Apr 2025 18:55:58 +0100
From: David Laight <david.laight.linux@...il.com>
To: Uros Bizjak <ubizjak@...il.com>
Cc: linux-um@...ts.infradead.org, x86@...nel.org,
 linux-kernel@...r.kernel.org, Richard Weinberger <richard@....at>, Anton
 Ivanov <anton.ivanov@...bridgegreys.com>, Johannes Berg
 <johannes@...solutions.net>, Thomas Gleixner <tglx@...utronix.de>, Ingo
 Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>, Dave Hansen
 <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] um/asm: Replace "REP; NOP" with PAUSE mnemonic

On Mon, 14 Apr 2025 16:55:57 +0200
Uros Bizjak <ubizjak@...il.com> wrote:

> Current minimum required version of binutils is 2.25,
> which supports PAUSE instruction mnemonic.
> 
> Replace "REP; NOP" with this proper mnemonic.
> 
> No functional change intended.
> 
> Signed-off-by: Uros Bizjak <ubizjak@...il.com>
> Cc: Richard Weinberger <richard@....at>
> Cc: Anton Ivanov <anton.ivanov@...bridgegreys.com>
> Cc: Johannes Berg <johannes@...solutions.net>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> ---
>  arch/x86/um/asm/processor.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/um/asm/processor.h b/arch/x86/um/asm/processor.h
> index 478710384b34..233a7a0d29c9 100644
> --- a/arch/x86/um/asm/processor.h
> +++ b/arch/x86/um/asm/processor.h
> @@ -24,7 +24,7 @@
>  /* REP NOP (PAUSE) is a good thing to insert into busy-wait loops. */
>  static __always_inline void rep_nop(void)
>  {
> -	__asm__ __volatile__("rep;nop": : :"memory");
> +	__asm__ __volatile__("pause": : :"memory");
>  }
>  

That only makes sense if you also change the function name.

	David

>  static __always_inline void cpu_relax(void)