linux-kernel - Re: [PATCH -tip] x86/locking/atomic: Use asm

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Message-ID: <20250305221806.7f25108f@pumpkin>
Date: Wed, 5 Mar 2025 22:18:06 +0000
From: David Laight <david.laight.linux@...il.com>
To: Uros Bizjak <ubizjak@...il.com>
Cc: Linus Torvalds <torvalds@...uxfoundation.org>, Borislav Petkov
 <bp@...en8.de>, Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, Thomas
 Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, Dave Hansen
 <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH -tip] x86/locking/atomic: Use asm_inline for atomic
 locking insns

On Wed, 5 Mar 2025 20:47:46 +0100
Uros Bizjak <ubizjak@...il.com> wrote:

...
> From the compiler POV, now that "lock; " prefix lost its semicolon,
> removing LOCK_PREFIX_HERE or using asm_inline would result in exactly
> the same code. The problematic 31k code size increase (1.1%) with -O2
> is inevitable either way, if we want to move forward.

Have you looked to see where that 31k comes from?
The compiler must be very near to inlining something and removing a couple
of instructions is making a big difference.
It is quite likely that some other change will have the same (or the reverse)
effect.

	David