From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail.zytor.com (terminus.zytor.com [198.137.202.136]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A7190E56A for ; Wed, 23 Oct 2024 21:41:53 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.137.202.136 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729719715; cv=none; b=MLIWvaUASFZddfanbWOtJ7/O0Rd/fDKosLwxZaL+aXoosYmBgxD2rKmGUWl+wvg+9DxHvIFE6SpI6T66hrl1d1I9slfGizqh3zrkF6vPZIIzk+iCXIxe3LdqL50V2v3rtLwRM8epU1aBOlg4G8nmY5C1O2kONCmJZ4GmeUHeKxE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729719715; c=relaxed/simple; bh=y4763EOgL1q3ScAtkoeUAWGIOBqiMl/Y29seYHxlJmU=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=owSk1ZZduIGsgUtfu3vgkQEJ0Gf/S3tPwitFdQM/ptGzA5/W6eajnxazCk6aPRAASz78yygNTbL0/DfC3oCqDjYVxtbRs1bTgMWLuV5EDJd2BiKBegevuq5C4vWPxPbmlDyWZHd9+jcKX3roi/Mh/dETsygh7q1Grg/I+YRp8Dw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com; spf=pass smtp.mailfrom=zytor.com; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b=Ru8OEuvY; arc=none smtp.client-ip=198.137.202.136 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=zytor.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=zytor.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=zytor.com header.i=@zytor.com header.b="Ru8OEuvY" Received: from [172.27.3.244] ([76.133.66.138]) (authenticated bits=0) by mail.zytor.com (8.18.1/8.17.1) with ESMTPSA id 49NLexNv1411797 (version=TLSv1.3 cipher=TLS_AES_128_GCM_SHA256 bits=128 verify=NO); Wed, 23 Oct 2024 14:40:59 -0700 DKIM-Filter: OpenDKIM Filter v2.11.0 mail.zytor.com 49NLexNv1411797 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=zytor.com; s=2024101701; t=1729719661; bh=bD0HK2j0SgBCID4Iw/rZZNpJTyJpExrZmV8kuJQazzo=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Ru8OEuvYgotG68bpU1jy5B2NhwpTi60EKtvz/WmX2nl2K0CUUMLvyQSxCWTWJT1ia 8/9H2rGjgd/Jq71UH78VZKB9SBhlbLTnV6Nt75oIgGcW8ahyBxJF6gZznS8ObG7+11 HBJCHCgW8J4ZxwmFL9Y4BhQUfGi//nLpxAv5Dxb5BbmAivTxgqVl2gFPG1pYn7dH3a pRMWpnJH8JWijyjWjGz0pWXC8oU7OISbUcrN4Xm/3ocjRMbYf0Xf/tI4cBCgjBirGg oV23LZZvXfSK5N8YQz+45gs5+neVUVtDZwGH8lJP2KCFeYeaTHlzf/4ii6QqutY/gj FPjIs/vi9ZWqA== Message-ID: <20ed1295-3012-4d71-a4d3-9d6a63cdfdf3@zytor.com> Date: Wed, 23 Oct 2024 14:40:59 -0700 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 1/1] x86/percpu: Cast -1 to argument type when comparing in percpu_add_op() To: Dave Hansen , "Christoph Lameter (Ampere)" Cc: Peter Zijlstra , Andy Shevchenko , Ingo Molnar , Uros Bizjak , linux-mm@kvack.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Dennis Zhou , Tejun Heo , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt References: <20240905170356.260300-1-andriy.shevchenko@linux.intel.com> <20241016192011.GY17263@noisy.programming.kicks-ass.net> <20241017181859.GB17263@noisy.programming.kicks-ass.net> <4b1a26b2-cccb-75d8-ee2f-f30ae211e598@gentwo.org> Content-Language: en-US From: "H. Peter Anvin" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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