From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 157FBC46CA3 for ; Tue, 5 Dec 2023 15:26:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1346158AbjLEP0R (ORCPT ); Tue, 5 Dec 2023 10:26:17 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33944 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346038AbjLEP0P (ORCPT ); Tue, 5 Dec 2023 10:26:15 -0500 Received: from mgamail.intel.com (mgamail.intel.com [192.55.52.115]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 408FA83 for ; Tue, 5 Dec 2023 07:26:22 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1701789982; x=1733325982; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=wRAIWeu2Gul6pnBzP7QzDoVc8X1qLMyprZgTMI6m47w=; b=iIBZNzUE/2HjmP6/Ml/dUJ8Y4sEzoP/LyvlAYSfIiZDbodZKNmNPkgBC EwDZ/ziYEyI6HSm+pB8j33NUCBXY5/fEgagPYgC/OCbb8qAgocZkAKa/D TQM7slSKieUXo5soX54B9RNmzySt6XqqN+eWM/d3NkmNEvmcJ3guv5qlv 32eaY6bfhH5UPST5gn8YGrZWMWSQqoEnp/UqZGiwHQjAQuGZolDxpO59V tCu2wLbObRyBP0Cvcm40a9O579mTmny+wAz6R4IprpmfPFHDIk6Nxd7Yk BFeCNsGj2e1C12WzLel3dEWlwZEstpY6D6EwDouWpI7uGsIk37v6AETh4 g==; X-IronPort-AV: E=McAfee;i="6600,9927,10915"; a="393642555" X-IronPort-AV: E=Sophos;i="6.04,252,1695711600"; d="scan'208";a="393642555" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Dec 2023 07:26:21 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10915"; a="836996222" X-IronPort-AV: E=Sophos;i="6.04,252,1695711600"; d="scan'208";a="836996222" Received: from nhickam-mobl.amr.corp.intel.com (HELO [10.255.230.231]) ([10.255.230.231]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Dec 2023 07:26:19 -0800 Message-ID: <2e7de96c-0634-4c98-9d56-ceba19c06c98@intel.com> Date: Tue, 5 Dec 2023 07:26:20 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] x86: intel_epb: Add earlyparam option to keep bias at performance Content-Language: en-US To: Jack Allister Cc: Paul Durrant , Jue Wang , Usama Arif , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Hans de Goede , Peter Zijlstra , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org References: <20231205131359.66338-1-jalliste@amazon.com> <20231205132355.76306-1-jalliste@amazon.com> 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: <20231205132355.76306-1-jalliste@amazon.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/5/23 05:23, Jack Allister wrote: > There are certain scenarios where it may be intentional that the EPB was > set at to 0/ENERGY_PERF_BIAS_PERFORMANCE on kernel boot. For example, in > data centers a kexec/live-update of the kernel may be performed regularly. > > Usually this live-update is time critical and defaulting of the bias back > to ENERGY_PERF_BIAS_NORMAL may actually be detrimental to the overall > update time if processors' time to ramp up/boost are affected. If this makes your kexecs 7 times faster, please say that here. Could we also please make this less wishy-washy? "May actually be detrimental" does not scream how critical this is for you. > This patch introduces a kernel command line "intel_epb_no_override" > which will leave the EPB at performance if during the restoration code path > it is detected as such. No "this patch", please: https://www.kernel.org/doc/html/next/process/maintainer-tip.html This also needs documentation of the parameter in Documentation/admin-guide/kernel-parameters.txt. Let me see if I can write a sane changelog, summarizing the discussion here for posterity. If there's confusion about a v1 patch that's cleared up in the discussion, it would be wonderful to capture that in the v2 changelog as opposed to making minimal changes. How's this? I think it captures some of the things that Rafael related and also additional information about the use case that motivated this effort. -- Buggy BIOSes set a sane boot-time Energy Performance Bias (EPB) that causes overheating. The kernel overrides any boot-time EPB "performance" bias to "normal" to avoid this. platforms can tolerate a "performance" bias during boot without overheating. In addition, because of , a kexec with a "normal" bias is seven times slower than "performance" to perform the kexec. Boot time is critical when performing a kexec/live-update of the kernel which is running guests VMs since boot time appears as guest latency or downtime. Introduce a command-line parameter, "intel_epb_no_override", to skip the "performance"=>"normal" override. This allows folks to get a speedy kexec without exposing other folks with wonky BIOSes to overheating.