| Message ID | 1533652024-19078-1-git-send-email-leo.yan@linaro.org |
|---|---|
| Headers | show |
| Series | Optimization CPU idle state impacted by tick | expand |
On Tue, Aug 07, 2018 at 10:27:02PM +0800, Leo Yan wrote: > After Rafael's patch series 'sched/cpuidle: Idle loop rework' has been > merged in mainline kernel, it perfectly resolved the Powernightmares > issue [1] with not stopping the tick during the idle loop; we verified > this patch series on Arm platform (96boards Hikey620 with octa CA53 > CPUs) with the rt-app [2] program to generate workloads: a single task > with below combinded configurations with period 5ms and duty cycle > 1%/3%/5%/10%/20%/30%/40%. Oops, I missed the two reference links, for complete info so list here: [1] https://tu-dresden.de/zih/forschung/ressourcen/dateien/projekte/haec/powernightmares.pdf?lang=en [2] https://git.linaro.org/power/rt-app.git Thanks, Leo Yan
After Rafael's patch series 'sched/cpuidle: Idle loop rework' has been merged in mainline kernel, it perfectly resolved the Powernightmares issue [1] with not stopping the tick during the idle loop; we verified this patch series on Arm platform (96boards Hikey620 with octa CA53 CPUs) with the rt-app [2] program to generate workloads: a single task with below combinded configurations with period 5ms and duty cycle 1%/3%/5%/10%/20%/30%/40%. After run these testing cases, we found the CPU cannot stay in deepest idle state as expected, the issues essentialy are related with sched tick: The prominent issue is the criteria for decision stopping tick; now the criteria is checking expected interval is less than TICK_USEC, but this doesn't consider from the perspective of idle state parameters, so we can observe the CPU even has enough sleeping time but it cannot run into deepest idle state; this is very serious for some specific ducy cycle cases. Another issue is after tick keeping running in idle state, the tick can heavily impact on 'menu' governor metrics, especially it will introduce many noise for next event correction factors. This patch series tries to fix these two issues; patch 0001 wants to define a time point to distinguish for stopping or not, this time point consideres the factors from tick period and the maximum target residency and use prediction period to compare this time point to decide if need to stop tick. Patch 0002 wants to always to give compensation for tick event so that dimiss the tick impaction on correction factors for next time prediction. Blow table are comparison results for testing cases between without and with this patch series; we run the test case with single task with period 5ms with different dutycycle, the total running time is 10s. Based on the tracing log, we do statistics for all CPUs for all idle states duration, the unit is second (s), on Hikey board the result shows the C2 state (the CPU deepest state) selection improvement. Some notations are used in the table: state: C0: WFI; C1: CPU OFF; C2: Cluster OFF All testing cases have single task with 5ms period: Without patches With patches Difference ----------------------------- ----------------------------- ------------------------------- Duty cycle C0 C1 C2 C0 C1 C2 C0 C1 C2 1% 0.218589 4.208460 87.995606 0.119723 0.847116 91.940569 -0.098866 -3.361344 +3.944963 3% 0.801521 5.031361 86.444753 0.147346 0.820276 91.761191 -0.654175 -4.211085 +5.316438 5% 0.590236 2.733048 88.284541 0.149237 1.042383 90.490482 -0.440999 -1.690665 +2.205941 10% 0.601922 6.282368 84.899870 0.169491 1.304985 89.725754 -0.432431 -4.977383 +4.825884 20% 1.381870 8.531687 80.627691 0.307390 3.302562 86.686887 -1.074480 -5.229125 +6.059196 30% 1.785221 6.974483 81.083312 0.548050 5.319929 83.551747 -1.237171 -1.654554 +2.468435 40% 1.403247 6.474203 80.577176 0.467686 6.366482 81.983384 -0.935561 -0.107721 +1.406208 Leo Yan (2): cpuidle: menu: Correct the criteria for stopping tick cpuidle: menu: Dismiss tick impaction on correction factors drivers/cpuidle/governors/menu.c | 55 ++++++++++++++++++++++++++++++++-------- 1 file changed, 45 insertions(+), 10 deletions(-) -- 2.7.4