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

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Message-ID: <22d90b7f-fdc9-40e3-8afb-c7bf313f60c2@zytor.com>
Date: Sat, 8 Mar 2025 11:15:00 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: Linus Torvalds <torvalds@...uxfoundation.org>,
        Uros Bizjak <ubizjak@...il.com>
Cc: 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>
Subject: Re: [PATCH -tip] x86/locking/atomic: Use asm_inline for atomic
 locking insns

On 3/5/25 09:04, Linus Torvalds wrote:
> 
> That said, I do want to bring up another issue: maybe it's time to
> just retire the LOCK_PREFIX thing entirely?
> 
> It harkens back to Ye Olde Days when UP was the norm, and we didn't
> want to pay the cost of lock prefixes when the kernel was built for
> SMP but was run on an UP machine.
> 
> And honestly, none of that makes sense any more. You can't buy a UP
> machine any more, and the only UP case would be some silly minimal
> virtual environment, and if people really care about that minimal
> case, they should just compile the kernel without SMP support.
> Becxause UP has gone from being the default to being irrelevant. At
> least for x86-64.
> 

I think the key there is that "they should just compile the kernel 
without SMP support" (which may very well make sense for some oddball 
embedded uses) *does* still mean that remaining cases of locks 
can/should be elided so demacroizing it is still not an option.

But yes... would get rid of a lot of crap machinery which is basically 
dead code, and that would be a Very Good Thing[TM].

	-hpa