From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.19]) (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 965AA1CF8B for ; Mon, 30 Mar 2026 16:58:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=198.175.65.19 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774889913; cv=none; b=eEj/OJUndc1wnRAZ2zbhl28D7fIkSvC26gNju9g/BXrVg5MzKFayGcB0twm1DIrqsYXOoewTidcRbTqsqf6f7jeToHQwrCnAaFaQtD06PBegH7R4AtXtbWu+BmeVwYb6uQqXdS+3Dl9D6y+5vNEJM6eoQkWWAjjWaEVyex7LMvs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774889913; c=relaxed/simple; bh=cXVcclGouA9TxBPRfcwgxoE3J2K9h6NExZPxLW7XJIU=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=LjaSEPVTkiy17x9qpK7wekcVCVHsRK7DngRG6+yIkqLpP5THRoNz+BzqChX3FpK3Xy92ATYmxZgF4QB3VZ4ExPSEh16qL5qfWiBZ+isHUZ1y+LPeVST18OVJMwTK4PY/PLITxVROLR5J4ee8zpTwPxPABvzHI1Zl+57fJXHzktc= 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=cjW8tGjY; arc=none smtp.client-ip=198.175.65.19 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="cjW8tGjY" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1774889910; x=1806425910; h=message-id:date:mime-version:subject:to:references:from: in-reply-to:content-transfer-encoding; bh=cXVcclGouA9TxBPRfcwgxoE3J2K9h6NExZPxLW7XJIU=; b=cjW8tGjYfQEYwat2XW/ST4gQV30zLE3PBOAfkfr6p76axxSbJ/7sd5Kj ImfEdBXkn9hjsLy1UfF8kREeIw90LN5I8ADhPnEcYUs7liKn8Yf7ifJyU MtSIePYBIeb/tvXJcSe3DDflm3dlD+k/Fu2mhmpt07kybCaGl/hu7TbVP pnRRekFtODt64x7jH5jdnVmHl3/zfT4LLzuwBAX6BLCvv3DYBhYJzyzAS IA12uFjNEBrSk6vvt7/nLiMeSxEA7MoTTk14KGGH2WKrUeTqjI2xecZEs Yfb4KR4adLJ54sVTZk3dfJZDsmNNvSIQbTpNfpo8CvciroDTYjTexcC42 w==; X-CSE-ConnectionGUID: iLFtOW3TTZWxUgsz6LQ0yQ== X-CSE-MsgGUID: qKpF71TYSYSdP+PQVUIdwA== X-IronPort-AV: E=McAfee;i="6800,10657,11743"; a="75776955" X-IronPort-AV: E=Sophos;i="6.23,150,1770624000"; d="scan'208";a="75776955" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by orvoesa111.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Mar 2026 09:58:30 -0700 X-CSE-ConnectionGUID: JRL9ryY7R4y9hJh/AakBSA== X-CSE-MsgGUID: RQseDBNfSMCJdP34owCOIQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,150,1770624000"; d="scan'208";a="219458169" Received: from sghuge-mobl2.amr.corp.intel.com (HELO [10.125.110.248]) ([10.125.110.248]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 30 Mar 2026 09:58:29 -0700 Message-ID: <2f763ca6-794e-4b5a-9b92-9a9cc8858cd2@intel.com> Date: Mon, 30 Mar 2026 09:58:35 -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 next] i386: Remove string functions that use 'rep scasb' To: david.laight.linux@gmail.com, Andrew Morton , Andy Shevchenko , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Uros Bizjak , linux-kernel@vger.kernel.org, Kees Cook , Linus Torvalds References: <20260327195747.89556-1-david.laight.linux@gmail.com> Content-Language: en-US From: Dave Hansen 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: <20260327195747.89556-1-david.laight.linux@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/27/26 12:57, david.laight.linux@gmail.com wrote: > The fixed overhead of all the 'rep xxx' instructions is rather more > that might expect. While 'rep movs' is getting better on more recent > CPU, the same is not true for 'rep scasb'. On my Zen-5 it has a > fixed overhead of 150 clocks and then takes 3 clocks for each byte. > I've not measured any Intel CPU, but the cost might be 'only' 40 + > 2n. One measurement on a modern 64-bit CPU isn't super convincing to me. > Remove the asm versions of strcat() strncat() strlen() memchr() > and memscan(), the generic C versions will be faster. > > It is quite likely that all these functions are slower than the generic > code on pretty much all CPU since the 486. This is rather handwavy for my taste. There seem to be two valid paths here: 1. We continue the "nobody cares about 32-bit" refrain. This removes a bunch of 32-bit-only code and complexity. If it causes a performance regression, we do not care much. 2. Someone makes _some_ kind of effort to test this on at least *one* 32-bit-only CPU to see if it does any harm. In other words, I'm not opposed to the patch, but the justification doesn't really work for me as written.