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([2a01:e34:ed2f:f020:10d8:56c2:f55d:11e3]) by smtp.googlemail.com with ESMTPSA id m11sm1325470wrn.92.2020.03.06.01.28.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Mar 2020 01:28:47 -0800 (PST) Subject: Re: [PATCH] sched: fair: Use the earliest break even To: Valentin Schneider Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , "open list:SCHEDULER" , Thomas Gleixner References: <20200304114844.17700-1-daniel.lezcano@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: <1bb2f7db-7f7f-506c-f4b3-22787c30931f@linaro.org> Date: Fri, 6 Mar 2020 10:28:46 +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-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Valentin, [cc'ing Thomas Gleixner] On 04/03/2020 19:31, Valentin Schneider wrote: > > On Wed, Mar 04 2020, Daniel Lezcano wrote: >>> With that said, that comment actually raises a valid point: picking >>> recently idled CPUs might give us warmer cache. So by using the break >>> even stat, we can end up picking CPUs with colder caches (have been >>> idling for longer) than the current logic would. I suppose more testing >>> will tell us where we stand. >> >> Actually I'm not sure this comment still applies. If the CPU is powered >> down, the cache is flushed or we can be picking up CPU with their cache >> totally trashed by interrupt processing. >> >>>> +++ b/kernel/sched/sched.h >>>> @@ -1015,6 +1015,7 @@ struct rq { >>>> #ifdef CONFIG_CPU_IDLE >>>> /* Must be inspected within a rcu lock section */ >>>> struct cpuidle_state *idle_state; >>>> + s64 break_even; >>> >>> Why signed? This should be purely positive, right? >> >> It should be, but s64 complies with the functions ktime_to_ns signature. >> >> static inline s64 ktime_to_ns(const ktime_t kt) >> > > Would there be harm then in simply storing: > > ktime_get_ns() + idle_state->exit_latency_ns > > (which is u64)? Actually I'm not sure, ktime_get_ns() is correct, it returns an u64 but it is actually returning: return ktime_to_ns(ktime_get()); where ktime_to_ns is returning a s64. There are the following functions: static inline u64 ktime_get_coarse_ns(void) static inline u64 ktime_get_coarse_real_ns(void) static inline u64 ktime_get_coarse_boottime_ns(void) static inline u64 ktime_get_coarse_clocktai_ns(void) static inline u64 ktime_get_ns(void) static inline u64 ktime_get_real_ns(void) static inline u64 ktime_get_boottime_ns(void) static inline u64 ktime_get_clocktai_ns(void) static inline u64 ktime_get_raw_ns(void) extern u64 ktime_get_mono_fast_ns(void); extern u64 ktime_get_raw_fast_ns(void); extern u64 ktime_get_boot_fast_ns(void); extern u64 ktime_get_real_fast_ns(void); They are all based on ktime_get_ns() which returns a s64. Not sure this type mismatch was done on purpose or not. Thomas? -- Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog