Backport the support for cluster scheduler level on Kunpeng Server · Pull Request !1275 · src-openEuler/kernel

#I4GEZS
#I88UKS
#I5W44S
The Kunpeng Server has cluster topology which was not supported by the mainline linux.
Now the support has been merged into mainline in v5.15.
https://lore.kernel.org/lkml/20210924085104.44806-1-21cnbao@gmail.com/

We'd like to backport the series to openEuler 20.03, in order to:

make scheduler build complete scheduler level on Kunpeng Server
enhance the performance in some cases

This PR has 3 series:

1st series: make kernel aware of cluster, expose cluster to sysfs
ABI and add SCHED_CLUSTER which can make load balance between clusters to
benefit lots of workload. This has been merged into mainline:
https://lore.kernel.org/lkml/20210924085104.44806-1-21cnbao@gmail.com/

2nd series: Fix two bugs in cluster scheduler
The details of the 2 bugs can by find in the follow link:
#I88UKS:【OLK-5.10】修复cluster调度域建立错误的场景

3rd series: This is the follow-up work to support cluster scheduler. Previously we
have added cluster level in the scheduler for both ARM64[1] and X86[2] to
support load balance between clusters to bring more memory bandwidth and
decrease cache contention. This patchset, on the other hand, takes care of
wake-up path by giving CPUs within the same cluster a try before scanning
the whole LLC to benefit those tasks communicating with each other.

| commitID     | 补丁名称                                                     | 回合是否冲突 | 冲突原因                                                     |
| ------------ | ------------------------------------------------------------ | ------------ | ------------------------------------------------------------ |
| c94a98a1de26| topology: Represent clusters of CPUs within a die            | 是           | Documentation的位置和格式发生变化。部分代码的相对位置发生变化 |
| 73796877f3e5| sched: Add cluster scheduler level in core and related Kconfig for ARM64 | 否           |                                                              |
| 8072124e989f| topology/sysfs: export cluster attributes only if an architectures has support | 是           | Documentaion的位置发生变化，按照4.19内核的原位置修改。部分代码发生重构，相对位置发生变化，基于4.19内核添加修改 |
| 68d8b00dca71| topology: Remove unused cpu_cluster_mask()                   | 否           |                                                              |
| 7f7344453623| arch_topology: Limit span of cpu_clustergroup_mask()         | 是           | 4.19内核到5.10内核存在重构，修改点所在的文件位置发生变化，基于4.19内核进行修改 |
| 91cf59f2bfe1| arch_topology: Make cluster topology span at least SMT CPUs  | 是           | 代码所在的文件位置发生变化，按照4.19内核中的原位置修改       |
| d99abce298f4 | sched: Add per_cpu cluster domain info and cpus_share_lowest_cache API | 是           | SD_CLUSTER的声明方式在4.19内核到5.10内核之间存在重构，这里使用4.19内核的声明方式 |
| 30fc24beff2a | sched/fair: Scan cluster before scanning LLC in wake-up path | 是           | select_idle_cpu这个函数在4.19内核到5.10内核之间存在重构，这里基于4.19内核的函数，修改patch的内容 |
| 302c73229a43 | scheduler: Create SDTL_SKIP flag to skip topology level      | 是           | 当前4.19分支的CONFIG_SCHED_SMT默认为n，需要考虑sched_cluster作为调度域最低层级的情况 |
| 39518365ec71 | sysctl: add a new register_sysctl_init() interface           | 是           | 增加新的依赖patch引入，新增一个register_sysctl_init()接口，部分代码位置发生变化 |
| 965864f440f0 | sched/topology, drivers/base/arch_topology: Rebuild the sched_domain hierarchy when capacities change | 是           | 增加新的依赖patch，删除部分用不到的功能，仅引入topology_update_cpu_topology这个函数 |
| 006c23c028be | sched/topology, arch/arm64: Rebuild the sched_domain hierarchy when the CPU capacity changes | 否           | 增加新的依赖patch，新增一个函数接口                          |
| 54062cb62d40 | scheduler: Add runtime knob sysctl_sched_cluster             | 是           | 部分代码的相对位置发生变化                                   |
| 57ed48e6a2f3 | scheduler: Add boot time enabling/disabling of cluster scheduling | 否           |                                                              |
| cab126264ad4 | scheduler: Disable cluster scheduling by default             | 否           |                                                              |
| 9714cea60665 | sched:Open the kernel configuration for cluster.             | 否           |                                                              |

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