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

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Message-ID: <20f1af22-71dc-4d62-9615-03030012222e@intel.com>
Date: Fri, 28 Feb 2025 08:48:30 -0800
From: Dave Hansen <dave.hansen@...el.com>
To: Uros Bizjak <ubizjak@...il.com>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <peterz@...radead.org>,
 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 -tip] x86/locking/atomic: Use asm_inline for atomic
 locking insns

On 2/28/25 04:35, Uros Bizjak wrote:
> The code size of the resulting x86_64 defconfig object file increases
> for 33.264 kbytes, representing 1.2% code size increase:
> 
>    text    data     bss     dec     hex filename
> 27450107        4633332  814148 32897587        1f5fa33 vmlinux-old.o
> 27483371        4633784  814148 32931303        1f67de7 vmlinux-new.o

So, first of all, thank you for including some objective measurement of
the impact if your patches. It's much appreciated.

But I think the patches need to come with a solid theory of why they're
good. The minimum bar for that, I think, is *some* kind of actual
real-world performance test. I'm not picky. Just *something* that spends
a lot of time in the kernel and ideally where a profile points at some
of the code you're poking here.

I'm seriously not picky: will-it-scale, lmbench, dbench, kernel
compiles. *ANYTHING*. *ANY* hardware. Run it on your laptop.

But performance patches need to come with performance *numbers*.