From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Lezcano Subject: Re: [PATCH v9 09/17] arm: tegra20: cpuidle: Handle case where secondary CPU hangs on entering LP2 Date: Fri, 21 Feb 2020 21:48:56 +0100 Message-ID: <21e3cc35-cc6b-5452-da93-bdaac43716c5@linaro.org> References: <20200212235134.12638-1-digetx@gmail.com> <20200212235134.12638-10-digetx@gmail.com> <20200221154318.GO10516@linaro.org> <239a2b66-8da8-2e6c-d19d-9ed207ad0a64@gmail.com> <20200221173649.GU10516@linaro.org>

<50a8fb7c-f497-2234-c0b0-560aec1c5691@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <50a8fb7c-f497-2234-c0b0-560aec1c5691-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> Content-Language: en-US Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Dmitry Osipenko Cc: Thierry Reding , Jonathan Hunter , Peter De Schrijver , "Rafael J. Wysocki" , =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Jasper Korten , David Heidelberg , Peter Geis , linux-pm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-tegra@vger.kernel.org On 21/02/2020 21:21, Dmitry Osipenko wrote: > 21.02.2020 23:02, Daniel Lezcano пишет: [ ... ] >>>>>>> + >>>>>>> + /* >>>>>>> + * The primary CPU0 core shall wait for the secondaries >>>>>>> + * shutdown in order to power-off CPU's cluster safely. >>>>>>> + * The timeout value depends on the current CPU frequency, >>>>>>> + * it takes about 40-150us in average and over 1000us in >>>>>>> + * a worst case scenario. >>>>>>> + */ >>>>>>> + do { >>>>>>> + if (tegra_cpu_rail_off_ready()) >>>>>>> + return 0; >>>>>>> + >>>>>>> + } while (ktime_before(ktime_get(), timeout)); >>>>>> >>>>>> So this loop will aggresively call tegra_cpu_rail_off_ready() and retry 3 >>>>>> times. The tegra_cpu_rail_off_ready() function can be called thoushand of times >>>>>> here but the function will hang 1.5s :/ >>>>>> >>>>>> I suggest something like: >>>>>> >>>>>> while (retries--i && !tegra_cpu_rail_off_ready()) >>>>>> udelay(100); >>>>>> >>>>>> So calls to tegra_cpu_rail_off_ready() and 100us x maximum >>>>>> impact. >>>>> But udelay() also results into CPU spinning in a busy-loop, and thus, >>>>> what's the difference? >>>> >>>> busy looping instead of register reads with all the hardware things involved behind. >>> >>> Please notice that this code runs only on an older Cortex-A9/A15, which >>> doesn't support WFE for the delaying, and thus, CPU always busy-loops >>> inside udelay(). >>> >>> What about if I'll add cpu_relax() to the loop? Do you think it it could >>> have any positive effect? >> >> I think udelay() has a call to cpu_relax(). > > Yes, my point is that udelay() doesn't bring much benefit for us here > because: > > 1. we want to enter into power-gated state as quick as possible and > udelay() just adds an unnecessary delay > > 2. udelay() spins in a busy-loop until delay is expired, just like we're > doing it in this function already In this case why not remove ktime_get() and increase the number of retries? -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog 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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 E3065C35666 for ; Fri, 21 Feb 2020 20:49:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A914D206EF for ; Fri, 21 Feb 2020 20:49:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="T52oE2jm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728144AbgBUUtB (ORCPT ); Fri, 21 Feb 2020 15:49:01 -0500 Received: from mail-wm1-f68.google.com ([209.85.128.68]:36184 "EHLO mail-wm1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726878AbgBUUtB (ORCPT ); Fri, 21 Feb 2020 15:49:01 -0500 Received: by mail-wm1-f68.google.com with SMTP id p17so3277560wma.1 for ; Fri, 21 Feb 2020 12:48:59 -0800 (PST) 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=KPj3sOpu0+HOby7nkRmHdqnlPkopY0WG1+4o7adp97Y=; b=T52oE2jmedGz9N+qNizC5i2LTDmtERO4J9SFkUhG/oB6IPuoB18TZ0WVDM5pO3kVLe H09O2/yOdY61/E0lKD67IQg+3g9mN0vfiLXNllxcT6pzRgTlWOMLgOk4QKYz6D2xm5Qt 0toN2Q9JTqmXJ4ktDxhG64r3ZDDy26JWGHYzcIWF+2XWr0Sj0MGCbPdm6+Zn5GNk1m2a +9TOrr3uGQyvIgGHjUJBVH+LHTH3W9Xo7da1+omqvbYAdqQAp3Cm9gt4tMtqgW6zqi8n pHuoK08yr6diDOxVcv3v7nN8umlvi4+02rAeRqVbs7GxlEuC/25H3VGsFt3f72xPrBfF wKbQ== 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=KPj3sOpu0+HOby7nkRmHdqnlPkopY0WG1+4o7adp97Y=; b=ka7Z6xVBgyGdBdeQo+vc4ZzTna7f3VpbO/IOYlVHam1sPNYuVAE1JPAw7d0m/S4uwh lqWnY+RGiDc5A7p2rMIafxpc4p+KFqZVX/GHSkKeglsO3RNwVMdEPsOwfpQr+pSuhjze LYToRjvYp/MP09SJDIb7NxOWm/Y9tF0RVBpn1tkLmEs0UpviccQXvfPwEuaraOu+L6ff kVn9vRT/0pGI67VrTqGj20Mw+b4cfgvtp41U9fBrQXjKPoTzXx663yE8UcuX7iiDzBpL GwjMjz2ElIRKpcd6cUXzx2xvV21xBW3vltk9o2p28sjPGVnRoCIyc3I4RuKaserSd+Sw dX5Q== X-Gm-Message-State: APjAAAXahfY+o+Wo3lTQkOeqydVY/hrkjqYC7geXReyc6RrKneOMRcCC 6bGBavlx0ADFuTwL2GRXvA9hvRwOt9w= X-Google-Smtp-Source: APXvYqwLEaYR+b3gSSws6RL6g0By5122418sCJ+S1+SZ0Yats1cK0ECqQTcl1gxvyFjpeS3iHjXMPw== X-Received: by 2002:a1c:a9c7:: with SMTP id s190mr5369150wme.97.1582318137938; Fri, 21 Feb 2020 12:48:57 -0800 (PST) Received: from ?IPv6:2a01:e34:ed2f:f020:903b:a048:f296:e3ae? ([2a01:e34:ed2f:f020:903b:a048:f296:e3ae]) by smtp.googlemail.com with ESMTPSA id c9sm5522721wrq.44.2020.02.21.12.48.56 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Feb 2020 12:48:57 -0800 (PST) Subject: Re: [PATCH v9 09/17] arm: tegra20: cpuidle: Handle case where secondary CPU hangs on entering LP2 To: Dmitry Osipenko Cc: Thierry Reding , Jonathan Hunter , Peter De Schrijver , "Rafael J. Wysocki" , =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= , Jasper Korten , David Heidelberg , Peter Geis , linux-pm@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org References: <20200212235134.12638-1-digetx@gmail.com> <20200212235134.12638-10-digetx@gmail.com> <20200221154318.GO10516@linaro.org> <239a2b66-8da8-2e6c-d19d-9ed207ad0a64@gmail.com> <20200221173649.GU10516@linaro.org>

<50a8fb7c-f497-2234-c0b0-560aec1c5691@gmail.com> 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: <21e3cc35-cc6b-5452-da93-bdaac43716c5@linaro.org> Date: Fri, 21 Feb 2020 21:48:56 +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: <50a8fb7c-f497-2234-c0b0-560aec1c5691@gmail.com> 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 On 21/02/2020 21:21, Dmitry Osipenko wrote: > 21.02.2020 23:02, Daniel Lezcano пишет: [ ... ] >>>>>>> + >>>>>>> + /* >>>>>>> + * The primary CPU0 core shall wait for the secondaries >>>>>>> + * shutdown in order to power-off CPU's cluster safely. >>>>>>> + * The timeout value depends on the current CPU frequency, >>>>>>> + * it takes about 40-150us in average and over 1000us in >>>>>>> + * a worst case scenario. >>>>>>> + */ >>>>>>> + do { >>>>>>> + if (tegra_cpu_rail_off_ready()) >>>>>>> + return 0; >>>>>>> + >>>>>>> + } while (ktime_before(ktime_get(), timeout)); >>>>>> >>>>>> So this loop will aggresively call tegra_cpu_rail_off_ready() and retry 3 >>>>>> times. The tegra_cpu_rail_off_ready() function can be called thoushand of times >>>>>> here but the function will hang 1.5s :/ >>>>>> >>>>>> I suggest something like: >>>>>> >>>>>> while (retries--i && !tegra_cpu_rail_off_ready()) >>>>>> udelay(100); >>>>>> >>>>>> So calls to tegra_cpu_rail_off_ready() and 100us x maximum >>>>>> impact. >>>>> But udelay() also results into CPU spinning in a busy-loop, and thus, >>>>> what's the difference? >>>> >>>> busy looping instead of register reads with all the hardware things involved behind. >>> >>> Please notice that this code runs only on an older Cortex-A9/A15, which >>> doesn't support WFE for the delaying, and thus, CPU always busy-loops >>> inside udelay(). >>> >>> What about if I'll add cpu_relax() to the loop? Do you think it it could >>> have any positive effect? >> >> I think udelay() has a call to cpu_relax(). > > Yes, my point is that udelay() doesn't bring much benefit for us here > because: > > 1. we want to enter into power-gated state as quick as possible and > udelay() just adds an unnecessary delay > > 2. udelay() spins in a busy-loop until delay is expired, just like we're > doing it in this function already In this case why not remove ktime_get() and increase the number of retries? -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog