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

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Message-ID: <CAFULd4ZtMrj+5Le0GArm5eTLw1AYiWLXPb_nXKaMDHy8TW60wA@mail.gmail.com>
Date: Wed, 16 Apr 2025 08:57:45 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: David Laight <david.laight.linux@...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 Wed, Apr 16, 2025 at 7:53 AM Uros Bizjak <ubizjak@...il.com> wrote:
>
> On Tue, Apr 15, 2025 at 7:56 PM David Laight
> <david.laight.linux@...il.com> wrote:
> >
> > 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.
>
> This function is used in several places, and is also defined for x86
> in arch/x86/include/asm/vdso/processor.h. The renaming should be
> coordinated with x86 and should definitely be a separate patch.

Something like the attached patch that also moves (duplicated)
function definition to a shared place.

Uros.

View attachment "pause.diff.txt" of type "text/plain" (2646 bytes)