From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.13]) (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 88898245B0B for ; Thu, 13 Feb 2025 20:48:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.13 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739479715; cv=none; b=opeZLPvpbf2GsJErIaKpxtPooLXR8p7zW/lSRRdcwhGKx75xHdbzCjMcFYEqyD3negku96SGawzz6dYd+RIGSyWJHOVlBr2FATiEbv3S6MGvr9qscqsmrWcOg4VOIx1fgnG/lF0XxE2H13lwy8nVJCNmlr1N9pmndqxCzRCMzmE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1739479715; c=relaxed/simple; bh=t6K3PCXljJZY/d7PpkUPcbHoIesQAQORXAmrHcizRJo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=PRWVNXSGOAYnjwA4OIox4OIMmVbIpvUH+tHxWllrRC5H4zG8goY29fJMTSDu5wSMy6X3ksrCc9Yv+QDyXPzCcoOYBBqihqj1hsGV5TGE5RF1428ARokPGfvFWyRSwPQ16YUl4xu20ZlzOoxRT3MFixVN+xe9JgEalyvld9S+AQo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=iza1QuuD; arc=none smtp.client-ip=192.198.163.13 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="iza1QuuD" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1739479713; x=1771015713; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=t6K3PCXljJZY/d7PpkUPcbHoIesQAQORXAmrHcizRJo=; b=iza1QuuD9WsERX7eWGmzHG1A7lgx5GLvMp1mtmTMscz8iPPpuKiNF81A mreH3+CtUx4Qu+M4aCMzl8v44+ffXh63vSgFrHLOWbYqinyFrWOsfDAbS rEp8n63YN22Ak+bVcBGBfn2Guok9flgzu8aFFxQbvi5u+ToS6qcS7N4S2 5/rRFHa3dFAQpmKhIZs0hYs8nYytyLReKWaJYHBeOmQwgoe+CuEyTEcuQ y5aUHJhDeYS396UFpaUOkdTWkCxKPFmbWaobO5DwgujRWZF6YW6UG4CYE CX67LCnXPhBI/oe2vrST0NQZp5K2Pec+x2oYAQuPPQ/rNMTQ+yeXVT6d6 g==; X-CSE-ConnectionGUID: +xAWfHPgQBaBtJeaHt0KlA== X-CSE-MsgGUID: 0j1B/dPPSwW4IUF9UZHXxg== X-IronPort-AV: E=McAfee;i="6700,10204,11344"; a="43042406" X-IronPort-AV: E=Sophos;i="6.13,282,1732608000"; d="scan'208";a="43042406" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by fmvoesa107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Feb 2025 12:48:33 -0800 X-CSE-ConnectionGUID: DG9NCrngTtGhi1HlZKjjvQ== X-CSE-MsgGUID: 7O41g2DPQPuJCNWyTGiaTA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.12,224,1728975600"; d="scan'208";a="117384013" Received: from iherna2-mobl4.amr.corp.intel.com (HELO [10.125.108.188]) ([10.125.108.188]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Feb 2025 12:48:32 -0800 Message-ID: <62965669-bf1d-461f-9401-20e303c6d619@intel.com> Date: Thu, 13 Feb 2025 12:48:31 -0800 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 RESEND 2/2] x86/locking: Use asm_inline for {,try_}cmpxchg{64,128} emulations To: Uros Bizjak , x86@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Dennis Zhou , Tejun Heo , Christoph Lameter , "Peter Zijlstra (Intel)" References: <20250213191457.12377-1-ubizjak@gmail.com> <20250213191457.12377-2-ubizjak@gmail.com> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; keydata= xsFNBE6HMP0BEADIMA3XYkQfF3dwHlj58Yjsc4E5y5G67cfbt8dvaUq2fx1lR0K9h1bOI6fC oAiUXvGAOxPDsB/P6UEOISPpLl5IuYsSwAeZGkdQ5g6m1xq7AlDJQZddhr/1DC/nMVa/2BoY 2UnKuZuSBu7lgOE193+7Uks3416N2hTkyKUSNkduyoZ9F5twiBhxPJwPtn/wnch6n5RsoXsb ygOEDxLEsSk/7eyFycjE+btUtAWZtx+HseyaGfqkZK0Z9bT1lsaHecmB203xShwCPT49Blxz VOab8668QpaEOdLGhtvrVYVK7x4skyT3nGWcgDCl5/Vp3TWA4K+IofwvXzX2ON/Mj7aQwf5W iC+3nWC7q0uxKwwsddJ0Nu+dpA/UORQWa1NiAftEoSpk5+nUUi0WE+5DRm0H+TXKBWMGNCFn c6+EKg5zQaa8KqymHcOrSXNPmzJuXvDQ8uj2J8XuzCZfK4uy1+YdIr0yyEMI7mdh4KX50LO1 pmowEqDh7dLShTOif/7UtQYrzYq9cPnjU2ZW4qd5Qz2joSGTG9eCXLz5PRe5SqHxv6ljk8mb ApNuY7bOXO/A7T2j5RwXIlcmssqIjBcxsRRoIbpCwWWGjkYjzYCjgsNFL6rt4OL11OUF37wL QcTl7fbCGv53KfKPdYD5hcbguLKi/aCccJK18ZwNjFhqr4MliQARAQABzUVEYXZpZCBDaHJp c3RvcGhlciBIYW5zZW4gKEludGVsIFdvcmsgQWRkcmVzcykgPGRhdmUuaGFuc2VuQGludGVs LmNvbT7CwXgEEwECACIFAlQ+9J0CGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEGg1 lTBwyZKwLZUP/0dnbhDc229u2u6WtK1s1cSd9WsflGXGagkR6liJ4um3XCfYWDHvIdkHYC1t MNcVHFBwmQkawxsYvgO8kXT3SaFZe4ISfB4K4CL2qp4JO+nJdlFUbZI7cz/Td9z8nHjMcWYF IQuTsWOLs/LBMTs+ANumibtw6UkiGVD3dfHJAOPNApjVr+M0P/lVmTeP8w0uVcd2syiaU5jB aht9CYATn+ytFGWZnBEEQFnqcibIaOrmoBLu2b3fKJEd8Jp7NHDSIdrvrMjYynmc6sZKUqH2 I1qOevaa8jUg7wlLJAWGfIqnu85kkqrVOkbNbk4TPub7VOqA6qG5GCNEIv6ZY7HLYd/vAkVY E8Plzq/NwLAuOWxvGrOl7OPuwVeR4hBDfcrNb990MFPpjGgACzAZyjdmYoMu8j3/MAEW4P0z F5+EYJAOZ+z212y1pchNNauehORXgjrNKsZwxwKpPY9qb84E3O9KYpwfATsqOoQ6tTgr+1BR CCwP712H+E9U5HJ0iibN/CDZFVPL1bRerHziuwuQuvE0qWg0+0SChFe9oq0KAwEkVs6ZDMB2 P16MieEEQ6StQRlvy2YBv80L1TMl3T90Bo1UUn6ARXEpcbFE0/aORH/jEXcRteb+vuik5UGY 5TsyLYdPur3TXm7XDBdmmyQVJjnJKYK9AQxj95KlXLVO38lczsFNBFRjzmoBEACyAxbvUEhd GDGNg0JhDdezyTdN8C9BFsdxyTLnSH31NRiyp1QtuxvcqGZjb2trDVuCbIzRrgMZLVgo3upr MIOx1CXEgmn23Zhh0EpdVHM8IKx9Z7V0r+rrpRWFE8/wQZngKYVi49PGoZj50ZEifEJ5qn/H Nsp2+Y+bTUjDdgWMATg9DiFMyv8fvoqgNsNyrrZTnSgoLzdxr89FGHZCoSoAK8gfgFHuO54B lI8QOfPDG9WDPJ66HCodjTlBEr/Cwq6GruxS5i2Y33YVqxvFvDa1tUtl+iJ2SWKS9kCai2DR 3BwVONJEYSDQaven/EHMlY1q8Vln3lGPsS11vSUK3QcNJjmrgYxH5KsVsf6PNRj9mp8Z1kIG qjRx08+nnyStWC0gZH6NrYyS9rpqH3j+hA2WcI7De51L4Rv9pFwzp161mvtc6eC/GxaiUGuH BNAVP0PY0fqvIC68p3rLIAW3f97uv4ce2RSQ7LbsPsimOeCo/5vgS6YQsj83E+AipPr09Caj 0hloj+hFoqiticNpmsxdWKoOsV0PftcQvBCCYuhKbZV9s5hjt9qn8CE86A5g5KqDf83Fxqm/ vXKgHNFHE5zgXGZnrmaf6resQzbvJHO0Fb0CcIohzrpPaL3YepcLDoCCgElGMGQjdCcSQ+Ci FCRl0Bvyj1YZUql+ZkptgGjikQARAQABwsFfBBgBAgAJBQJUY85qAhsMAAoJEGg1lTBwyZKw l4IQAIKHs/9po4spZDFyfDjunimEhVHqlUt7ggR1Hsl/tkvTSze8pI1P6dGp2XW6AnH1iayn yRcoyT0ZJ+Zmm4xAH1zqKjWplzqdb/dO28qk0bPso8+1oPO8oDhLm1+tY+cOvufXkBTm+whm +AyNTjaCRt6aSMnA/QHVGSJ8grrTJCoACVNhnXg/R0g90g8iV8Q+IBZyDkG0tBThaDdw1B2l asInUTeb9EiVfL/Zjdg5VWiF9LL7iS+9hTeVdR09vThQ/DhVbCNxVk+DtyBHsjOKifrVsYep WpRGBIAu3bK8eXtyvrw1igWTNs2wazJ71+0z2jMzbclKAyRHKU9JdN6Hkkgr2nPb561yjcB8 sIq1pFXKyO+nKy6SZYxOvHxCcjk2fkw6UmPU6/j/nQlj2lfOAgNVKuDLothIxzi8pndB8Jju KktE5HJqUUMXePkAYIxEQ0mMc8Po7tuXdejgPMwgP7x65xtfEqI0RuzbUioFltsp1jUaRwQZ MTsCeQDdjpgHsj+P2ZDeEKCbma4m6Ez/YWs4+zDm1X8uZDkZcfQlD9NldbKDJEXLIjYWo1PH hYepSffIWPyvBMBTW2W5FRjJ4vLRrJSUoEfJuPQ3vW9Y73foyo/qFoURHO48AinGPZ7PC7TF vUaNOTjKedrqHkaOcqB185ahG2had0xnFsDPlx5y In-Reply-To: <20250213191457.12377-2-ubizjak@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 2/13/25 11:14, Uros Bizjak wrote: > According to [1], the usage of asm pseudo directives in the asm template > can confuse the compiler to wrongly estimate the size of the generated > code. ALTERNATIVE macro expands to several asm pseudo directives, so > its usage in {,try_}cmpxchg{64,128} causes instruction length estimate > to fail by an order of magnitude (the compiler estimates the length of > an asm to be more than 20 instructions). Just curious, but how did you come up with the "20 instructions" number? > This wrong estimate further causes unoptimal inlining decisions for > functions that use these locking primitives. > > Use asm_inline instead of just asm. For inlining purposes, the size of > the asm is then taken as the minimum size, ignoring how many instructions > compiler thinks it is. So, the compiler is trying to decide whether to inline a function or not. The bigger it is, the less likely, it is to be inlined. Since it is over-estimating the size of {,try_}cmpxchg{64,128}, it will avoid inlining it when it _should_ be inlining it. Is that it? Is any of this measurable? Is there any objective data to support that this change is a good one? It's quite possible that someone did the "asm" on purpose because over-estimating the size was a good thing.