From: "H. Peter Anvin" <hpa@zytor.com>
To: Dave Hansen <dave.hansen@intel.com>,
"Christoph Lameter (Ampere)" <cl@gentwo.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
Ingo Molnar <mingo@kernel.org>, Uros Bizjak <ubizjak@gmail.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
llvm@lists.linux.dev, Dennis Zhou <dennis@kernel.org>,
Tejun Heo <tj@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>
Subject: Re: [PATCH v1 1/1] x86/percpu: Cast -1 to argument type when comparing in percpu_add_op()
Date: Wed, 23 Oct 2024 14:40:59 -0700 [thread overview]
Message-ID: <20ed1295-3012-4d71-a4d3-9d6a63cdfdf3@zytor.com> (raw)
In-Reply-To: <bc707fc1-b5fe-4c2d-af88-c44737198876@intel.com>
On 10/23/24 10:15, Dave Hansen wrote:
> 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.
Do we really? I don't know if there are any microarchitectures where the
partial register update still matters. It is only one byte difference.
-hpa
next prev parent reply other threads:[~2024-10-23 21:41 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-05 17:03 Andy Shevchenko
2024-10-16 13:37 ` Andy Shevchenko
2024-10-16 15:44 ` Dave Hansen
2024-10-16 17:03 ` Nick Desaulniers
2024-10-16 18:06 ` Andy Shevchenko
2024-10-16 18:20 ` Andy Shevchenko
2024-10-16 19:43 ` Dave Hansen
2024-10-16 19:20 ` Peter Zijlstra
2024-10-16 19:44 ` Dave Hansen
2024-10-17 18:18 ` Peter Zijlstra
2024-10-18 12:21 ` Andy Shevchenko
2024-10-22 19:53 ` Dave Hansen
2024-10-22 23:24 ` Christoph Lameter (Ampere)
2024-10-23 17:15 ` Dave Hansen
2024-10-23 21:40 ` H. Peter Anvin [this message]
2024-10-23 14:24 ` Andy Shevchenko
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