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description/open_source: introduce ANDROID

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---
title: ANDROID 系统
date: 2021-02-15 00:32
author: gatieme
tags:
- linux
- tools
categories:
- 技术积累
thumbnail:
blogexcerpt: ANDROID
---
<br>
本作品采用<a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">知识共享署名-非商业性使用-相同方式共享 4.0 国际许可协议</a>进行许可, 转载请注明出处, 谢谢合作
<a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/"><img alt="知识共享许可协议" style="border-width:0" src="https://i.creativecommons.org/l/by-nc-sa/4.0/88x31.png" /></a>
因本人技术水平和知识面有限, 内容如有纰漏或者需要修正的地方, 欢迎大家指正, 鄙人在此谢谢啦
**转载请务必注明出处, 谢谢, 不胜感激**
<br>
| 日期 | 作者 | GitHub| CSDN | BLOG |
| ------- |:-------:|:-------:|:-------:|:-------:|
| 2021-02-15 | [成坚-gatieme](https://kernel.blog.csdn.net) | [`AderXCoding/system/tools/fzf`](https://github.com/gatieme/AderXCoding/tree/master/system/tools/fzf) | [使用模糊搜索神器 FZF 来提升办公体验](https://blog.csdn.net/gatieme/article/details/113828826) | [Using FZF to Improve Productivit](https://oskernellab.com/2021/02/15/2021/0215-0001-Using_FZF_to_Improve_Productivity)|
<br>
2 **ANDROID 系统**
=====================
**-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*　重要功能和时间点　-*-*-*-*-*-*-*-*-*-*-*-*-*-*-***
下文将按此目录分析 Linux 内核中 MM 的重要功能和引入版本:
**-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* 正文 -*-*-*-*-*-*-*-*-*-*-*-*-*-*-***
# 1 SCHED
-------
## 1.1 OPPO oplus_scheduler
-------
| feature | sysfs interface |
|:-------:|:---------------:|
| oplus_scheduler | OPLUS_SCHEDASSIST_PROC_DIR |
| slide_boost | OPLUS_SLIDEBOOST_PROC_DIR |
| sched_assist | OPLUS_SCHEDASSIST_PROC_DIR |
### 1.1.1 Sched Assist
-------
OPPO 通过 global_sched_assist_scene 进行场景标记和感知. 然后通过 sched_assist_scene() 获取到当前所属的场景.
| CONFIG | 描述 | 源代码路径 | 代表手机 | 芯片平台 |
|:------:|:---:|:---------:|:------:|:-------:|
| CONFIG_OPLUS_FEATURE_SCHED_ASSIST | |
| CONFIG_OPLUS_FEATURE_SCHED_SPREAD | nr-balance to spread tasks | `kernel/sched/oem_sched/oem_fair`<br>`vendor/oplus/kernel/oplus_performance_5.10/misc/sched_assist`<br>`kernel/oplus_perf_sched/sched_assist` | OPPO FindX5 Pro | Snapdragon 8 Gen 1, QCOM-5.10, ColorOS 12.1 PFEM10_11_A.18 |
#### 1.1.1.1 SCHED_ASSIST
-------
#### 1.1.1.2 SCHED_SPREAD
-------
CONFIG_OPLUS_FEATURE_SCHED_SPREAD 实现了一个仅通过 nr_running 数量来进行分级选核和负载均衡的策略, 无需跟踪 TASK 和 RQ 的实际负载信息, 因此更快速, overhead 更低.
> PS.
> 这种算法我们之前在服务器场景也曾经尝试过, 当时是为了 BYPASS 负载均衡和选核的 overload.
> 不过当时的数据库业务场景, 并没有看到明显的收益.
oplus_task_struct->lb_state 记录了进程的负载状态 high 或者 low. 每次 WALT 更新进程的负载信息时, 根据进程的负载信息动态更新.
```cpp
walt_update_task_ravg()
update_task_demand()
update_history()
-=> update_load_flag()
```
PER_CPU(task_lb_count) 记录了各个 cpu cgroup 分组 high 负载和 low 负载的任务数量. 每次进程入队和出队的时候, 根据进程的 cgroup 信息 `task_lb_sched_type()` 和其负载信息(high 或者 low), 通过 inc_ld_stats()/dec_ld_stats() 维护 task_lb_count 计数.
```cpp
enqueue_task()
-=> trace_android_rvh_after_enqueue_task(rq, p) =======> android_rvh_enqueue_task()
-=> inc_rq_walt_stats(rq, p)
-=> dec_ld_stats(p, rq)
dequeue_task()
-=> trace_android_rvh_after_dequeue_task(rq, p) =======> android_rvh_dequeue_task()
-=> dec_rq_walt_stats(rq, p)
-=> dec_ld_stats(p, rq)
```
选核时候, 通过 sched_assist_spread_tasks() 按照 nr_running(也就是 PER_CPU(task_lb_count)) 来选核, 寻找到 rq_nr/lowest_nr 最小的 CPU. lowest_nr 相同时则选择 NR 加权负载 rq_nr_load 最小的.
```cpp
walt_find_energy_efficient_cpu()
-=> walt_find_best_target()
-=> sched_assist_spread_tasks(p, new_allowed_cpus, fbt_env->order_index, fbt_env->end_index, fbt_env->skip_cpu, candidates, fbt_env->strict_max)
-=> find_spread_lowest_nr_cpu(p, &visit_cpus, sched_type, prev_cpu, skip_cpu, &lowest_nr, &lowest_nr_load, &lowest_nr_cpu)
-=> if (fbt_env.fastpath == NR_WAKEUP_SELECT) best_energy_cpu = cpumask_first(candidates)
```
其中 rq_nr_load 直接已 nr_running 做加权来预估 CPU 的负载, 不同 sched_type 的 nr_running 权重不同.
$rq_nr_load = 1000 \times ux_nr + 100 \times top_nr + 10 \times fg_nr + bg_nr$
# 2 MM
-------
# 3 ANDROID
-------
<br>
* 本作品/博文 ( [AderStep-紫夜阑珊-青伶巷草 Copyright ©2013-2017](http://blog.csdn.net/gatieme) ), 由 [成坚(gatieme)](http://blog.csdn.net/gatieme) 创作.
* 采用<a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/"><img alt="知识共享许可协议" style="border-width:0" src="https://i.creativecommons.org/l/by-nc-sa/4.0/88x31.png" /></a><a rel="license" href="http://creativecommons.org/licenses/by-nc-sa/4.0/">知识共享署名-非商业性使用-相同方式共享 4.0 国际许可协议</a>进行许可. 欢迎转载、使用、重新发布, 但务必保留文章署名[成坚gatieme](http://blog.csdn.net/gatieme) ( 包含链接: http://blog.csdn.net/gatieme ), 不得用于商业目的.
* 基于本文修改后的作品务必以相同的许可发布. 如有任何疑问, 请与我联系.
* **转载请务必注明出处, 谢谢, 不胜感激**
<br>
study/kernel/00-DESCRIPTION/SCHEDULER.md
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@@ -3280,7 +3280,7 @@ v3.0 版本 [sched: Reduce runqueue lock contention -v6](https://git.kernel.org/
| 2015/08/03 | tip-bot for Peter Zijlstra <tipbot@zytor.com> | [sched: Introduce the 'trace_sched_waking' tracepoint](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=fbd705a0c6184580d0e2fbcbd47a37b6e5822511) | NA | v1 ☑✓ 4.3-rc1 | [LORE](https://lore.kernel.org/all/tip-fbd705a0c6184580d0e2fbcbd47a37b6e5822511@git.kernel.org/) |
| 2020/05/24 | Mel Gorman | [Optimise try_to_wake_up() when wakee is descheduling](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/log/?id=2ebb17717550607bcd85fb8cf7d24ac870e9d762) | 唤醒时如果 wakee 进程正在睡眠或者调度(释放 CPU), 优化在 on_cpu 的自旋等待时间 | v1 ☑ 5.8-rc1 | [LORE 0/2](https://lore.kernel.org/lkml/20200524202956.27665-1-mgorman@techsingularity.net) |
| 2022/08/24 | Peng Wang <rocking@linux.alibaba.com> | [sched/fair: select waker's cpu for wakee on sync wakeup](https://lore.kernel.org/all/1508aa17d1a169077c8d8d8c22d2bd529101af0e.1661313074.git.rocking@linux.alibaba.com) | TODO | v1 ☐☑✓ | [LORE](https://lore.kernel.org/all/1508aa17d1a169077c8d8d8c22d2bd529101af0e.1661313074.git.rocking@linux.alibaba.com) |
| 2022/09/16 | Chen Yu <yu.c.chen@intel.com> | [sched/fair: Choose the CPU where short task is running during wake up](https://lore.kernel.org/all/20220915165407.1776363-1-yu.c.chen@intel.com) | TODO | v1 ☐☑✓ | [LORE](https://lore.kernel.org/all/20220915165407.1776363-1-yu.c.chen@intel.com) |
| 2022/09/16 | Chen Yu <yu.c.chen@intel.com> | [sched/fair: Choose the CPU where short task is running during wake up](https://lore.kernel.org/all/20220915165407.1776363-1-yu.c.chen@intel.com) | TODO | v1 ☐☑✓ | [LORE](https://lore.kernel.org/all/20220915165407.1776363-1-yu.c.chen@intel.com)<br>*-*-*-*-*-*-*-* <br>[LORE v2,0/2](https://lore.kernel.org/all/cover.1666531576.git.yu.c.chen@intel.com/) |
### 4.7.1.1 TTWU 中的内存屏障