linux-kernel - Re: [PATCH v1 1/1] x86/percpu: Cast -1 to argument type when comparing in percpu_add

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Message-ID: <bc707fc1-b5fe-4c2d-af88-c44737198876@intel.com>
Date: Wed, 23 Oct 2024 10:15:12 -0700
From: Dave Hansen <dave.hansen@...el.com>
To: "Christoph Lameter (Ampere)" <cl@...two.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
 Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Ingo Molnar <mingo@...nel.org>, Uros Bizjak <ubizjak@...il.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
 Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling
 <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Subject: Re: [PATCH v1 1/1] x86/percpu: Cast -1 to argument type when
 comparing in percpu_add_op()

On 10/22/24 16:24, Christoph Lameter (Ampere) wrote:
> On Tue, 22 Oct 2024, Dave Hansen wrote:
> 
>> So I think Peter's version was the best.  It shuts up clang and also
>> preserves the existing (good) gcc 'sub' behavior.  I'll send it out for
>> real in a bit, but I'm thinking of something like the attached patch.
> The desired behavior is a "dec". "sub" has a longer op code AFAICT.

Gah, yes, of course.  I misspoke.

We want "inc" and "dec" for +1 and -1.  "add" and "sub" are heftier and
get used for everything else.