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([2a01:e34:ed2f:f020:903b:a048:f296:e3ae]) by smtp.googlemail.com with ESMTPSA id o77sm5483841wme.34.2020.02.21.12.02.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 21 Feb 2020 12:02:31 -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> 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: Date: Fri, 21 Feb 2020 21:02:30 +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: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org On 21/02/2020 19:19, Dmitry Osipenko wrote: > 21.02.2020 20:36, Daniel Lezcano пишет: >> On Fri, Feb 21, 2020 at 07:56:51PM +0300, Dmitry Osipenko wrote: >>> Hello Daniel, >>> >>> 21.02.2020 18:43, Daniel Lezcano пишет: >>>> On Thu, Feb 13, 2020 at 02:51:26AM +0300, Dmitry Osipenko wrote: >>>>> It is possible that something may go wrong with the secondary CPU, in that >>>>> case it is much nicer to get a dump of the flow-controller state before >>>>> hanging machine. >>>>> >>>>> Acked-by: Peter De Schrijver >>>>> Tested-by: Peter Geis >>>>> Tested-by: Jasper Korten >>>>> Tested-by: David Heidelberg >>>>> Signed-off-by: Dmitry Osipenko >>>>> --- >> >> [ ... ] >> >>>>> +static int tegra20_wait_for_secondary_cpu_parking(void) >>>>> +{ >>>>> + unsigned int retries = 3; >>>>> + >>>>> + while (retries--) { >>>>> + ktime_t timeout = ktime_add_ms(ktime_get(), 500); >>>> >>>> Oops I missed this one. Do not use ktime_get() in this code path, use jiffies. >>> >>> Could you please explain what benefits jiffies have over the ktime_get()? >> >> ktime_get() is very slow, jiffies is updated every tick. > > But how jiffies are supposed to be updated if interrupts are disabled? Yeah, other cpus must not be idle in this. > Aren't jiffies actually slower than ktime_get() because jiffies are > updating every 10/1ms (depending on CONFIG_HZ)? They are no slower, they have a lower resolution which is 10ms or 4ms. Given the 500ms timeout, it is fine. > We're kinda interesting here in getting into deep-idling state as quick > as possible. I was checking how much time takes the busy-loop below and > it takes ~40-150us in average, which is good enough. ktime_get() gets a seq lock and it is very slow. >>>>> + >>>>> + /* >>>>> + * 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(). -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog