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 X-Spam-Level: X-Spam-Status: No, score=-7.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F23A7C10DCE for ; Wed, 18 Mar 2020 11:04:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AF4562076D for ; Wed, 18 Mar 2020 11:04:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="A3iniDuz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727566AbgCRLE6 (ORCPT ); Wed, 18 Mar 2020 07:04:58 -0400 Received: from mail-wr1-f68.google.com ([209.85.221.68]:40831 "EHLO mail-wr1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726733AbgCRLE6 (ORCPT ); Wed, 18 Mar 2020 07:04:58 -0400 Received: by mail-wr1-f68.google.com with SMTP id f3so22783838wrw.7 for ; Wed, 18 Mar 2020 04:04:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=subject:to:cc:references:from:autocrypt:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=KRvo2AnedhxVnlA+EvDsxLitXemLLTPkBYA0yM+Px8k=; b=A3iniDuzEsg/eOraikmeaGfeS8BAtq8n/r2TJhOob3fbPinvCMJZqot6XhNJS7gjT8 SRLE8h4aTjWt5IqeosWSw3lPeqkEXNJAQF5T+dZ9yfz0egfdQCmrQ2mhITil1jwdTC6f dwL/4CO/+fuA0E06AFPBet2Gw7rad+MQ+YT9QdlaAMR6syBuf+M/3BUv9BW02yXpzpiC 6DjMP3ycqR5UU0BVfehHtokqxSA2sJD4x9QNErf2bu80BuWMmVz2KzwoOpzMngRENa7D Nx6/W0TPzG+zaneLuHou/yVpBnVbEeNYxf2H/wGwTJqLbRpwAkPTBIEWdezD8oWotxAC lpwg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=KRvo2AnedhxVnlA+EvDsxLitXemLLTPkBYA0yM+Px8k=; b=VsuRQhZgOXN2o3ODRzpGT91nyGwfdiKpBYGt0OSkCHSC2qQaV+waIl0xqT2mAVSgr8 H2iN+prinTAPGit/6CczOAr7IEYH/baN/eswwHn31uNw0IKWuEjebYJEQzJrChwbG46g 8QdTcdP7Yg1W+DlvZItxb63isMCr6WYKE+013oATNPDHCW+DrJHRDVrtsz69l4943HVp 45NNPmuA0bsrTfXq9+wHPyIMFccKWnPVIR2vQExKmuRzxGdBj9+K0DK/V1muiX4xxfcR 1TnVUadWoCcA8WjIxVmDek/TGRzu6uAZoD1W0SXq2kIVs+va0+T/qeqmKvn4xoODqcLF bjAw== X-Gm-Message-State: ANhLgQ3H/fT9045nzqOZFv5n5wpBXqocjp+vFPcfDF3HXqUZe6UhwF+b 0ajb6VA3HL1HFCqhZJO1nEdURQ== X-Google-Smtp-Source: ADFU+vsEPKKXoNLrq+h0rJ8LJoWmrZKw/KUI31whkpkBF+U46kfttWy+6DZ/dB4m0yuOw1/R5LrALA== X-Received: by 2002:a5d:52d0:: with SMTP id r16mr4822813wrv.379.1584529495406; Wed, 18 Mar 2020 04:04:55 -0700 (PDT) Received: from ?IPv6:2a01:e34:ed2f:f020:bd37:618d:f415:31ea? ([2a01:e34:ed2f:f020:bd37:618d:f415:31ea]) by smtp.googlemail.com with ESMTPSA id b5sm8747529wrw.86.2020.03.18.04.04.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Mar 2020 04:04:54 -0700 (PDT) Subject: Re: [PATCH RFC] cpuidle: consolidate calls to time capture To: "Rafael J. Wysocki" Cc: ulf.hansson@linaro.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, khilman@kernel.org References: <20200316210843.11678-1-daniel.lezcano@linaro.org> <2605374.f08NWHE4iP@kreacher> From: Daniel Lezcano Autocrypt: addr=daniel.lezcano@linaro.org; prefer-encrypt=mutual; keydata= xsFNBFv/yykBEADDdW8RZu7iZILSf3zxq5y8YdaeyZjI/MaqgnvG/c3WjFaunoTMspeusiFE sXvtg3ehTOoyD0oFjKkHaia1Zpa1m/gnNdT/WvTveLfGA1gH+yGes2Sr53Ht8hWYZFYMZc8V 2pbSKh8wepq4g8r5YI1XUy9YbcTdj5mVrTklyGWA49NOeJz2QbfytMT3DJmk40LqwK6CCSU0 9Ed8n0a+vevmQoRZJEd3Y1qXn2XHys0F6OHCC+VLENqNNZXdZE9E+b3FFW0lk49oLTzLRNIq 0wHeR1H54RffhLQAor2+4kSSu8mW5qB0n5Eb/zXJZZ/bRiXmT8kNg85UdYhvf03ZAsp3qxcr xMfMsC7m3+ADOtW90rNNLZnRvjhsYNrGIKH8Ub0UKXFXibHbafSuq7RqyRQzt01Ud8CAtq+w P9EftUysLtovGpLSpGDO5zQ++4ZGVygdYFr318aGDqCljKAKZ9hYgRimPBToDedho1S1uE6F 6YiBFnI3ry9+/KUnEP6L8Sfezwy7fp2JUNkUr41QF76nz43tl7oersrLxHzj2dYfWUAZWXva wW4IKF5sOPFMMgxoOJovSWqwh1b7hqI+nDlD3mmVMd20VyE9W7AgTIsvDxWUnMPvww5iExlY eIC0Wj9K4UqSYBOHcUPrVOKTcsBVPQA6SAMJlt82/v5l4J0pSQARAQABzSpEYW5pZWwgTGV6 Y2FubyA8ZGFuaWVsLmxlemNhbm9AbGluYXJvLm9yZz7Cwa4EEwEIAEECGwEFCwkIBwIGFQoJ CAsCBBYCAwECHgECF4ACGQEWIQQk1ibyU76eh+bOW/SP9LjScWdVJwUCXAkeagUJDRnjhwAh CRCP9LjScWdVJxYhBCTWJvJTvp6H5s5b9I/0uNJxZ1Un69gQAJK0ODuKzYl0TvHPU8W7uOeu U7OghN/DTkG6uAkyqW+iIVi320R5QyXN1Tb6vRx6+yZ6mpJRW5S9fO03wcD8Sna9xyZacJfO UTnpfUArs9FF1pB3VIr95WwlVoptBOuKLTCNuzoBTW6jQt0sg0uPDAi2dDzf+21t/UuF7I3z KSeVyHuOfofonYD85FkQJN8lsbh5xWvsASbgD8bmfI87gEbt0wq2ND5yuX+lJK7FX4lMO6gR ZQ75g4KWDprOO/w6ebRxDjrH0lG1qHBiZd0hcPo2wkeYwb1sqZUjQjujlDhcvnZfpDGR4yLz 5WG+pdciQhl6LNl7lctNhS8Uct17HNdfN7QvAumYw5sUuJ+POIlCws/aVbA5+DpmIfzPx5Ak UHxthNIyqZ9O6UHrVg7SaF3rvqrXtjtnu7eZ3cIsfuuHrXBTWDsVwub2nm1ddZZoC530BraS d7Y7eyKs7T4mGwpsi3Pd33Je5aC/rDeF44gXRv3UnKtjq2PPjaG/KPG0fLBGvhx0ARBrZLsd 5CTDjwFA4bo+pD13cVhTfim3dYUnX1UDmqoCISOpzg3S4+QLv1bfbIsZ3KDQQR7y/RSGzcLE z164aDfuSvl+6Myb5qQy1HUQ0hOj5Qh+CzF3CMEPmU1v9Qah1ThC8+KkH/HHjPPulLn7aMaK Z8t6h7uaAYnGzjMEXZLIEhYJKwYBBAHaRw8BAQdAGdRDglTydmxI03SYiVg95SoLOKT5zZW1 7Kpt/5zcvt3CwhsEGAEIACAWIQQk1ibyU76eh+bOW/SP9LjScWdVJwUCXZLIEgIbAgCvCRCP 9LjScWdVJ40gBBkWCAAdFiEEbinX+DPdhovb6oob3uarTi9/eqYFAl2SyBIAIQkQ3uarTi9/ eqYWIQRuKdf4M92Gi9vqihve5qtOL396pnZGAP0c3VRaj3RBEOUGKxHzcu17ZUnIoJLjpHdk NfBnWU9+UgD/bwTxE56Wd8kQZ2e2UTy4BM8907FsJgAQLL4tD2YZggwWIQQk1ibyU76eh+bO W/SP9LjScWdVJ5CaD/0YQyfUzjpR1GnCSkbaLYTEUsyaHuWPI/uSpKTtcbttpYv+QmYsIwD9 8CeH3zwY0Xl/1fE9Hy59z6Vxv9YVapLx0nPDOA1zDVNq2MnutxHb8t+Imjz4ERCxysqtfYrv gao3E/h0c8SEeh+bh5MkjwmU8CwZ3doWyiVdULKESe7/Gs5OuhFzaDVPCpWdsKdCAGyUuP/+ qRWwKGVpWP0Rrt6MTK24Ibeu3xEZO8c3XOEXH5d9nf6YRqBEIizAecoCr00E9c+6BlRS0AqR OQC3/Mm7rWtco3+WOridqVXkko9AcZ8AiM5nu0F8AqYGKg0y7vkL2LOP8us85L0p57MqIR1u gDnITlTY0x4RYRWJ9+k7led5WsnWlyv84KNzbDqQExTm8itzeZYW9RvbTS63r/+FlcTa9Cz1 5fW3Qm0BsyECvpAD3IPLvX9jDIR0IkF/BQI4T98LQAkYX1M/UWkMpMYsL8tLObiNOWUl4ahb PYi5Yd8zVNYuidXHcwPAUXqGt3Cs+FIhihH30/Oe4jL0/2ZoEnWGOexIFVFpue0jdqJNiIvA F5Wpx+UiT5G8CWYYge5DtHI3m5qAP9UgPuck3N8xCihbsXKX4l8bdHfziaJuowief7igeQs/ WyY9FnZb0tl29dSa7PdDKFWu+B+ZnuIzsO5vWMoN6hMThTl1DxS+jc7ATQRb/8z6AQgAvSkg 5w7dVCSbpP6nXc+i8OBz59aq8kuL3YpxT9RXE/y45IFUVuSc2kuUj683rEEgyD7XCf4QKzOw +XgnJcKFQiACpYAowhF/XNkMPQFspPNM1ChnIL5KWJdTp0DhW+WBeCnyCQ2pzeCzQlS/qfs3 dMLzzm9qCDrrDh/aEegMMZFO+reIgPZnInAcbHj3xUhz8p2dkExRMTnLry8XXkiMu9WpchHy XXWYxXbMnHkSRuT00lUfZAkYpMP7La2UudC/Uw9WqGuAQzTqhvE1kSQe0e11Uc+PqceLRHA2 bq/wz0cGriUrcCrnkzRmzYLoGXQHqRuZazMZn2/pSIMZdDxLbwARAQABwsGNBBgBCAAgFiEE JNYm8lO+nofmzlv0j/S40nFnVScFAlv/zPoCGwwAIQkQj/S40nFnVScWIQQk1ibyU76eh+bO W/SP9LjScWdVJ/g6EACFYk+OBS7pV9KZXncBQYjKqk7Kc+9JoygYnOE2wN41QN9Xl0Rk3wri qO7PYJM28YjK3gMT8glu1qy+Ll1bjBYWXzlsXrF4szSqkJpm1cCxTmDOne5Pu6376dM9hb4K l9giUinI4jNUCbDutlt+Cwh3YuPuDXBAKO8YfDX2arzn/CISJlk0d4lDca4Cv+4yiJpEGd/r BVx2lRMUxeWQTz+1gc9ZtbRgpwoXAne4iw3FlR7pyg3NicvR30YrZ+QOiop8psWM2Fb1PKB9 4vZCGT3j2MwZC50VLfOXC833DBVoLSIoL8PfTcOJOcHRYU9PwKW0wBlJtDVYRZ/CrGFjbp2L eT2mP5fcF86YMv0YGWdFNKDCOqOrOkZVmxai65N9d31k8/O9h1QGuVMqCiOTULy/h+FKpv5q t35tlzA2nxPOX8Qj3KDDqVgQBMYJRghZyj5+N6EKAbUVa9Zq8xT6Ms2zz/y7CPW74G1GlYWP i6D9VoMMi6ICko/CXUZ77OgLtMsy3JtzTRbn/wRySOY2AsMgg0Sw6yJ0wfrVk6XAMoLGjaVt X4iPTvwocEhjvrO4eXCicRBocsIB2qZaIj3mlhk2u4AkSpkKm9cN0KWYFUxlENF4/NKWMK+g fGfsCsS3cXXiZpufZFGr+GoHwiELqfLEAQ9AhlrHGCKcgVgTOI6NHg== Message-ID: <669fe03f-0d65-8ca9-53dc-1323e0397c53@linaro.org> Date: Wed, 18 Mar 2020 12:04:52 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <2605374.f08NWHE4iP@kreacher> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Rafael, On 18/03/2020 11:17, Rafael J. Wysocki wrote: > On Monday, March 16, 2020 10:08:43 PM CET Daniel Lezcano wrote: >> A few years ago, we changed the code in cpuidle to replace ktime_get() >> by a local_clock() to get rid of potential seq lock in the path and an >> extra latency. >> >> Meanwhile, the code evolved and we are getting the time in some other >> places like the power domain governor and in the future break even >> deadline proposal. > > Hmm? > > Have any patches been posted for that? https://lkml.org/lkml/2020/3/11/1113 https://lkml.org/lkml/2020/3/13/466 but there is no consensus yet if that has a benefit or not. >> Unfortunately, as the time must be compared across the CPU, we have no >> other option than using the ktime_get() again. Hopefully, we can >> factor out all the calls to local_clock() and ktime_get() into a >> single one when the CPU is entering idle as the value will be reuse in >> different places. > > So there are cases in which it is not necessary to synchronize the time > between CPUs and those would take the overhead unnecessarily. > > This change looks premature to me at least. The idea is to call one time ktime_get() when entering idle and store the result in the struct cpuidle_device, so we have the information when we entered idle. Moreover, ktime_get() is called in do_idle() via: tick_nohz_idle_enter() tick_nohz_start_idle() ts->idle_entrytime = ktime_get(); This is called at the first loop level. The idle loop is exiting and re-entering again without passing through tick_nohz_idle_enter() in the second loop level in case of interrupt processing, thus the idle_entrytime is not updated and the return of tick_nohz_get_sleep_length() will be greater than what is expected. May be we can consider ktime_get_mono_fast_ns() which is lockless with a particular care of the non-monotonic aspect if needed. Given the description at [1] the time jump could a few nanoseconds in case of NMI. The local_clock() can no be inspected across CPUs, the gap is too big and continues to increase during system lifetime. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/time/timekeeping.c#n396 -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog