From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.18]) (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 5B4811BD9E2; Fri, 8 Nov 2024 16:14:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731082464; cv=none; b=YHm9mekWenoE4Il/gKcHTB3VBF2uDw65Rf/2SArh6mogwhMPaFBL2h8jURiWb/FHGVGKMOcd4bXm/UC2fjLGXZ6cNmhiW4wQlq35u6plu5DIll91y3oYrH98/lP/l5yJrEANB65g+g4H+P1LJy7upDaSMCULaaTk9BDOK6/mLyU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731082464; c=relaxed/simple; bh=43Ia+a7MU+429mSA3hhjnIzSQdrT7VEYniLDvOPEEvQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=esoPGeJwZXtmjxcXX0m0HNzMKLe4BT+XtePF5x8bo/3rMIE/4MVeDcFR381k4XyIAREfRfw1Pm5VN+wW9lzX56NYt/e4auczcCJyhEbt09rTaQTm9BcysMAhPpZhTbO4Zi2MCaIP/XMgdCQyJeV3QXQF31XiTn2DyaubIQTpopg= 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=RVyrzGRz; arc=none smtp.client-ip=192.198.163.18 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="RVyrzGRz" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1731082463; x=1762618463; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=43Ia+a7MU+429mSA3hhjnIzSQdrT7VEYniLDvOPEEvQ=; b=RVyrzGRzsWHg0ZZ7q2qc7TEcqGcVOYdSr3G658vSzS2P6i3WcRaJb/Ai 2OyeQp1iq2Ri65t2P/x76KfZD3v+L1yoeB5aXaJvgLD5f0ys1pb7YkqFq T6y9p/l/HZfhf+7A1fMJEgiGtB+sbAVDWeMxZ4yKWhgJS9e/dS26yVgfY h3O/eEG3u93MaXNaRAX5/UvuJ8zxpkonDlHkm8BUOAfoDRjGiUsFj6zaQ sP87yn1CqLKcb4fR4cArdeCMsE+aZ0VyutZkvKQqlq42C+NuVsi/TY2zb 8J1gVF0mKqjcC53OhL8nNEpHzU2T0w0RRh11XXefUthRKGuQxLVodo6cz A==; X-CSE-ConnectionGUID: fNR10v0gTNyblG/E44cq6w== X-CSE-MsgGUID: dctZwBp/QsqS3uiE1+Qaqg== X-IronPort-AV: E=McAfee;i="6700,10204,11250"; a="30386537" X-IronPort-AV: E=Sophos;i="6.12,138,1728975600"; d="scan'208";a="30386537" Received: from fmviesa008.fm.intel.com ([10.60.135.148]) by fmvoesa112.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Nov 2024 08:14:23 -0800 X-CSE-ConnectionGUID: Bjo465FrTj2bdIWxPHQZ6g== X-CSE-MsgGUID: Km6xKbgaRyi0l8MfaeqCiA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.12,138,1728975600"; d="scan'208";a="85773591" Received: from rfrazer-mobl3.amr.corp.intel.com (HELO [10.124.223.66]) ([10.124.223.66]) by fmviesa008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Nov 2024 08:14:22 -0800 Message-ID: <394fa854-41a9-4ad1-880b-629108d52b41@intel.com> Date: Fri, 8 Nov 2024 08:14:21 -0800 Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play_dead() To: Patryk Wlazlyn , x86@kernel.org Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, rafael.j.wysocki@intel.com, len.brown@intel.com, artem.bityutskiy@linux.intel.com, dave.hansen@linux.intel.com References: <20241108122909.763663-1-patryk.wlazlyn@linux.intel.com> <20241108122909.763663-3-patryk.wlazlyn@linux.intel.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: <20241108122909.763663-3-patryk.wlazlyn@linux.intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/8/24 04:29, Patryk Wlazlyn wrote: > The generic implementation, based on cpuid leaf 0x5, for looking up the > mwait hint for the deepest cstate, depends on them to be continuous in > range [0, NUM_SUBSTATES-1]. While that is correct on most Intel x86 > platforms, it is not architectural and may not result in reaching the > most optimized idle state on some of them. > > Prefer cpuidle_play_dead() over the generic mwait_play_dead() loop and > fallback to the later in case of missing enter_dead() handler. I don't think the bug has anything to do with this patch, really. There's no need to rehash it here. The issue here is that the only way to call mwait today is via mwait_play_dead() directly, using its internally-calculated hint. What you want is for a cpuidle-driver-calculated hint to be used. So, you're using the new hint function via the cpuidle driver. But you just need the cpuidle driver to be called first, not the old mwait_play_dead()-calculated hint. The new code will still do mwait, just via a different path and with a different hint. The thing this doesn't mention is what the impact on everyone else is. I _think_ the ACPI cpuidle driver is the only worry. Today, if there's a system that supports mwait and ACPI cpuidle, it'll use mwait. After this patch, it'll use ACPI cpuidle. The changelog doesn't mention that behavior change or why that's OK. Also, looking at this: > - mwait_play_dead(); > if (cpuidle_play_dead()) > - hlt_play_dead(); > + mwait_play_dead(); > + hlt_play_dead(); None of those return on success, right? Is there any reason this couldn't just be: /* The first successful play_dead() will not return: */ cpuidle_play_dead(); mwait_play_dead(); hlt_play_dead(); That has the added bonus of not needing to return anything from mwait_play_dead() and the resulting churn from the last patch.