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: <20241017181859.GB17263@noisy.programming.kicks-ass.net>
Date: Thu, 17 Oct 2024 20:18:59 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: 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>, Christoph Lameter <cl@...ux.com>,
	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 Wed, Oct 16, 2024 at 12:44:18PM -0700, Dave Hansen wrote:

> Would anybody hate if we broke this up a bit, like:
> 
>         const typeof(var) _val = val;
>         const int paoconst = __builtin_constant_p(val);
>         const int paoinc   = paoconst && ((_val) == 1);
>         const int paodec   = paoconst && ((_val) == (typeof(var))-1);
> 
> and then did
> 
> 	if (paoinc)
> 		percpu_unary_op(size, qual, "inc", var);
> 	...

I think that is an overall improvement. Proceed! :-)