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Date: Wed, 6 Jan 2016 16:22:52 +0100 From: Daniel Lezcano <daniel.lezcano@...aro.org> To: tglx@...utronix.de, peterz@...radead.org, rafael@...nel.org Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org, nicolas.pitre@...aro.org, vincent.guittot@...aro.org Subject: [RFC PATCH 0/2] IRQ based next prediction The current approach to select an idle state is based on the idle period statistics computation. Useless to say this approach satisfied everyone as a solution to find the best trade-off between the performances and the energy saving via the menu governor. However, the kernel is evolving to act pro-actively regarding the energy constraints with the scheduler and the different power management subsystems are not collaborating with the scheduler as the conductor of the decisions, they all act independently. The cpuidle governors are based on idle period statistics, without knowledge of what woke up the cpu. In these sources of wakes up, the IPI are of course accounted (as well as the timers irq) which results in doing statistics on the scheduler behavior too. It is no sense to let the scheduler to take a decision based on a next prediction of its own decisions. In order to integrate the cpuidle framework into the scheduler, we have to radically change the approach by clearly identifying what is causing a wake up and how it behaves. This serie inverts the logic. Instead of tracking the idle durations and do statistics on them, these patches track the interrupt individually and try to predict the next interrupt. By combining the interrupts' next event on a single CPU, we can predict the next event for the CPU, hence predict how long we will be sleeping when entering idle. The IPI and timer interrupts are not taken into account. The first patch provides a callback to be registered in the irq subsystem and to be called when an interrupt is handled with a timestamp. The second patch uses the callback provided by the patch above to compute the delta and store it in a circular buffer. It is per cpu, the callback implements minimal operations as it is in an interrupt context. When we the cpu enters idle, it asks for the expected sleep time. Then the expected minimum sleep length for all interrupts is used and compared to the timer sleep length, again the minimum is taken and gives the expected sleep time. The statistics are very trivial and could be improved later but this first step shows we have a nice overall improvement in SMP. In UP the menu governor is a bit better which may indicate the next prediction computation could be improved but confirms removing the IPI from the equation increase the accuracy. These are the results with a workload emulator (mp3, video, browser, ...) on a Dual Xeon 6 cores. Each test has been run 10 times. The results are based on a debugfs statistics where, when we exit idle, we check if the idle state was the right one which gives a successful prediction even if the exact wakeup time is not correct. The error margin is absorbed by the idle state's target residency, eg. idle1 is 10 us, idle2 is 50us, idle3 is 150us, if we predict to sleep 110us but at the end we sleep 80us, the prediction is still successful as the idle2 is the correct one for 80us and 110us. (mean colum - 5th -, greater is better). SMP (12 cores): -------------------------- Successful predictions (%) -------------------------- scripts/iolatsimu.sh.menu.dat: N min max sum mean stddev 10 30.96 39.3 346.15 34.615 2.37729 scripts/iolatsimu.sh.irq.dat: N min max sum mean stddev 10 22.21 54.39 377.1 37.71 11.3374 -------------------------- Successful predictions (%) -------------------------- scripts/fio-aio.sh.menu.dat: N min max sum mean stddev 10 44.32 48.81 459.5 45.95 1.59114 scripts/fio-aio.sh.irq.dat: N min max sum mean stddev 10 54.18 64.75 592.86 59.286 2.83509 -------------------------- Successful predictions (%) -------------------------- scripts/fio-cpuio.sh.menu.dat: N min max sum mean stddev 10 86.86 91 890.21 89.021 1.34882 scripts/fio-cpuio.sh.irq.dat: N min max sum mean stddev 10 97.97 98.57 981.85 98.185 0.171804 -------------------------- Successful predictions (%) -------------------------- scripts/fio-zipf.sh.menu.dat: N min max sum mean stddev 10 87.58 94.53 917.07 91.707 1.81287 scripts/fio-zipf.sh.irq.dat: N min max sum mean stddev 10 95.51 98.88 980.25 98.025 1.06026 -------------------------- Successful predictions (%) -------------------------- scripts/fio-netio.sh.menu.dat: N min max sum mean stddev 10 65.51 81.82 729.41 72.941 5.34134 scripts/fio-netio.sh.irq.dat: N min max sum mean stddev 10 97.38 97.88 976.19 97.619 0.162238 -------------------------- Successful predictions (%) -------------------------- scripts/fio-falloc.sh.menu.dat: N min max sum mean stddev 10 79.4 91.58 858.71 85.871 3.51946 scripts/fio-falloc.sh.irq.dat: N min max sum mean stddev 10 65.06 87.54 728.72 72.872 6.29703 -------------------------- Successful predictions (%) -------------------------- scripts/fio-null.sh.menu.dat: N min max sum mean stddev 10 89.44 92.83 908.96 90.896 1.12064 scripts/fio-null.sh.irq.dat: N min max sum mean stddev 10 95.68 98.74 978.19 97.819 0.954468 -------------------------- Successful predictions (%) -------------------------- scripts/rt-app-browser.sh.menu.dat: N min max sum mean stddev 10 59 67.66 640.21 64.021 3.11123 scripts/rt-app-browser.sh.irq.dat: N min max sum mean stddev 10 81.45 91.48 865.2 86.52 3.39756 -------------------------- Successful predictions (%) -------------------------- scripts/rt-app-mp3.sh.menu.dat: N min max sum mean stddev 10 65.85 70.67 674.85 67.485 1.34196 scripts/rt-app-mp3.sh.irq.dat: N min max sum mean stddev 10 94.97 97.24 963.96 96.396 0.743897 -------------------------- Successful predictions (%) -------------------------- scripts/rt-app-video.sh.menu.dat: N min max sum mean stddev 10 59.41 63.14 615.57 61.557 1.24713 scripts/rt-app-video.sh.irq.dat: N min max sum mean stddev 10 70.92 76.8 747.7 74.77 1.84455 -------------------------- Successful predictions (%) -------------------------- scripts/video.sh.menu.dat: N min max sum mean stddev 10 27.99 35.54 302.23 30.223 2.27853 scripts/video.sh.irq.dat: N min max sum mean stddev 10 54.42 72.42 635.55 63.555 6.48589 -------------------------- Successful predictions (%) -------------------------- scripts/netperf.sh.menu.dat: N min max sum mean stddev 10 67.49 82.46 748.43 74.843 4.64976 scripts/netperf.sh.irq.dat: N min max sum mean stddev 10 97.51 99.43 990.12 99.012 0.545768 In UP: -------------------------- Successful predictions (%) -------------------------- scripts/iolatsimu.sh.menu.dat: N min max sum mean stddev 10 49.5 55.66 514.02 51.402 2.31278 scripts/iolatsimu.sh.irq.dat: N min max sum mean stddev 10 39.49 63.51 552.35 55.235 6.54344 -------------------------- Successful predictions (%) -------------------------- scripts/fio-aio.sh.menu.dat: N min max sum mean stddev 10 49.44 51.9 502.44 50.244 0.849552 scripts/fio-aio.sh.irq.dat: N min max sum mean stddev 10 35.58 42.06 381.57 38.157 2.05544 -------------------------- Successful predictions (%) -------------------------- scripts/fio-cpuio.sh.menu.dat: N min max sum mean stddev 10 93.07 97.26 954.71 95.471 1.52628 scripts/fio-cpuio.sh.irq.dat: N min max sum mean stddev 10 91.02 97.48 943.92 94.392 2.21478 -------------------------- Successful predictions (%) -------------------------- scripts/fio-zipf.sh.menu.dat: N min max sum mean stddev 10 76.92 88 831.94 83.194 3.2838 scripts/fio-zipf.sh.irq.dat: (2 runs without idle transitions) N min max sum mean stddev 8 50 100 657.5 82.1875 22.418 -------------------------- Successful predictions (%) -------------------------- scripts/fio-netio.sh.menu.dat: N min max sum mean stddev 10 78.95 85.71 818.7 81.87 2.01494 scripts/fio-netio.sh.irq.dat: N min max sum mean stddev 10 62.5 90 733.51 73.351 7.77129 -------------------------- Successful predictions (%) -------------------------- scripts/fio-falloc.sh.menu.dat: N min max sum mean stddev 10 29.42 38.46 357.83 35.783 2.57226 scripts/fio-falloc.sh.irq.dat: N min max sum mean stddev 10 28.85 37.48 333.22 33.322 3.121 -------------------------- Successful predictions (%) -------------------------- scripts/fio-null.sh.menu.dat: N min max sum mean stddev 10 73.53 84.62 806.44 80.644 3.57214 scripts/fio-null.sh.irq.dat: N min max sum mean stddev 10 57.14 85.71 761.68 76.168 8.73407 -------------------------- Successful predictions (%) -------------------------- scripts/rt-app-browser.sh.menu.dat: N min max sum mean stddev 10 96.33 98.8 976.84 97.684 0.834921 scripts/rt-app-browser.sh.irq.dat: N min max sum mean stddev 10 93.02 100 984.58 98.458 2.08916 -------------------------- Successful predictions (%) -------------------------- scripts/rt-app-mp3.sh.menu.dat: N min max sum mean stddev 10 99.06 99.59 993.8 99.38 0.178948 scripts/rt-app-mp3.sh.irq.dat: N min max sum mean stddev 10 95.81 99.54 978.95 97.895 1.36267 -------------------------- Successful predictions (%) -------------------------- scripts/rt-app-video.sh.menu.dat: N min max sum mean stddev 10 96.96 99.08 983.25 98.325 0.632899 scripts/rt-app-video.sh.irq.dat: N min max sum mean stddev 10 74.77 97.5 829.45 82.945 7.10247 -------------------------- Successful predictions (%) -------------------------- scripts/video.sh.menu.dat: N min max sum mean stddev 10 48.52 59.73 541.3 54.13 3.11611 scripts/video.sh.irq.dat: N min max sum mean stddev 10 43.71 58.5 533.62 53.362 4.84646 Daniel Lezcano (2): irq: Add a framework to measure interrupt timings sched: idle: IRQ based next prediction for idle period drivers/cpuidle/Kconfig | 5 + include/linux/interrupt.h | 45 ++++ include/linux/irqdesc.h | 3 + kernel/irq/Kconfig | 3 + kernel/irq/handle.c | 12 + kernel/irq/manage.c | 65 +++++- kernel/sched/Makefile | 1 + kernel/sched/idle-sched.c | 553 ++++++++++++++++++++++++++++++++++++++++++++++ 8 files changed, 686 insertions(+), 1 deletion(-) create mode 100644 kernel/sched/idle-sched.c -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at 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