linux-kernel - Re: [PATCH v7 RESEND 5/6] arm64: futex: small optimisation for __llsc_futex_atomic

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Message-ID: <aMRMBEdro1YJ5RLW@arm.com>
Date: Fri, 12 Sep 2025 17:36:20 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Yeoreum Yun <yeoreum.yun@....com>
Cc: Will Deacon <will@...nel.org>, broonie@...nel.org, maz@...nel.org,
	oliver.upton@...ux.dev, joey.gouly@....com, james.morse@....com,
	ardb@...nel.org, scott@...amperecomputing.com,
	suzuki.poulose@....com, yuzenghui@...wei.com, mark.rutland@....com,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 RESEND 5/6] arm64: futex: small optimisation for
 __llsc_futex_atomic_set()

On Thu, Sep 11, 2025 at 05:19:11PM +0100, Yeoreum Yun wrote:
> > > +static __always_inline int
> > > +__llsc_futex_atomic_set(int oparg, u32 __user *uaddr, int *oval)
[...]
> > Hmm, I'm really not sure this is worthwhile. I doubt the "optimisation"
> > actually does anything and adding a whole new block of asm just for the
> > SET case isn't much of an improvement on the maintainability side, either.
> 
> TBH, I had the same question, but I thought this code seems to modify
> freqenetly, I decide even a small optimisation -- reduce one instruction
> only.
> 
> But I don't have strong opinion for this patch.
> If it's not good for maintainability perspective,
> This patch can be dropped.

I'd drop it for now unless you can show some performance benefits
(unlikely).

-- 
Catalin