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Cheng Jian
2021-10-06 17:59:28 +08:00
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@@ -600,7 +600,7 @@ https://lore.kernel.org/lkml/157476581065.5793.4518979877345136813.stgit@buzz/
最早的时候是 Valentin Schneider 在 HUAWEI KunPeng 920 上发现了一个问题, 构建调度域的过程中在部分 CPU 构建时 报了 `ERROR: groups don't span domain->span`. 参见 [sched/topology: Fix overlapping sched_group build](https://lore.kernel.org/lkml/20200324125533.17447-1-valentin.schneider@arm.com). 这台机器由 2 socket(每个 scoker 由 2 个 DIE 组成, 每个 DIE 包含 24 个 CPU).
社区经过讨论发现, 这是由于内核当前调度域构建的方式存在诸多限制, 对超过 2 个 NUMA 层级的系统支持不完善. 暂时没有想到好的解决方法. 因此 Valentin Schneider 决定先通过 WARN_ON 警告此问题 [sched/topology: Warn when NUMA diameter > 2](https://lore.kernel.org/lkml/20201110184300.15673-1-valentin.schneider@arm.com).
社区经过讨论发现, 这是由于内核当前调度域构建的方式存在诸多限制, 对超过 2 个 NUMA 层级的系统支持不完善. 因此我们称这个问题为 3 跳问题(3 htops)暂时没有想到好的解决方法. 因此 Valentin Schneider 决定先通过 WARN_ON 警告此问题 [sched/topology: Warn when NUMA diameter > 2](https://lore.kernel.org/lkml/20201110184300.15673-1-valentin.schneider@arm.com).
@@ -616,12 +616,28 @@ https://lore.kernel.org/lkml/157476581065.5793.4518979877345136813.stgit@buzz/
|:----:|:-----:|:-------:|
| 2021/1/21 | Meelis Roos | [Shortest NUMA path spans too many nodes](https://lkml.org/lkml/2021/1/21/726) |
3-hops 目前来看存在两个问题:
1. sched_init_numa() 中在构建 numa 距离表的时候, 假定以 NODE 0 为起点的距离阶梯包含了系统中所有节点的距离步长. 这种假定在以 NODE 0 为边缘结点的 NUMA 系统中工作的很好, 但是对于不以 NODE 0 为边缘结点的 NUMA 系统中并不适用. 这会造成以 NODE 0 构建的 NUMA 距离表缺失了一部分距离, 造成真正的边缘结点缺失了一层调度域, 并没有包含系统中所有的结点.
```cpp
以 0 为结点的 NUMA 系统 :
2 10 2
0 <---> 1 <---> 2 <---> 3
以 1 为结点的 NUMA 系统 :
2 10 2
1 <---> 0 <---> 2 <---> 3
```
2. build_overlap_sched_groups() 中构建顶层调度域时, 为边缘节点构建高层级调度域时, 当前域中可能只想包含 3 个结点, 但是 sched_group 却意外的把另外一个结点也包含进来了. 从而造成上报了 `ERROR: groups don't span domain->span` 等错误.
| 时间 | 作者 | 特性 | 描述 | 是否合入主线 | 链接 |
|:----:|:----:|:--:|:----:|:---------:|:----:|
| 2021/01/22 | Valentin Schneider | [sched/topology: NUMA distance deduplication](https://lore.kernel.org/patchwork/cover/1369363) | 修复 | v1 ☑ 5.12-rc1 | [PatchWork](https://lore.kernel.org/patchwork/cover/1369363), [LKML](https://lkml.org/lkml/2021/1/22/460), [commit](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=620a6dc40754dc218f5b6389b5d335e9a107fd29) |
| 2021/01/15 | Song Bao Hua (Barry Song) | [sched/fair: first try to fix the scheduling impact of NUMA diameter > 2](https://lore.kernel.org/patchwork/patch/1366256) | 尝试修复 3 跳问题导致的性能蜕化 | RFC | [PatchWork](https://lore.kernel.org/patchwork/cover/1366256) |
| 2021/01/27 | Song Bao Hua (Barry Song) | [sched/topology: fix the issue groups don't span domain->span for NUMA diameter > 2](https://lore.kernel.org/patchwork/patch/1371875)| 修复 | v2 | [PatchWork](https://lore.kernel.org/patchwork/cover/1371875), [LKML]() |
| 2021/01/22 | Valentin Schneider | [sched/topology: NUMA distance deduplication](https://lore.kernel.org/patchwork/cover/1369363) | 修复问题 1 | v1 ☑ 5.12-rc1 | [PatchWork](https://lore.kernel.org/patchwork/cover/1369363), [LKML](https://lkml.org/lkml/2021/1/22/460), [commit](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=620a6dc40754dc218f5b6389b5d335e9a107fd29) |
| 2021/01/15 | Song Bao Hua (Barry Song) | [sched/fair: first try to fix the scheduling impact of NUMA diameter > 2](https://lore.kernel.org/patchwork/patch/1366256) | 修复问题 2 | RFC ☐ | [PatchWork](https://lore.kernel.org/patchwork/cover/1366256) |
| 2021/2/23q | Song Bao Hua (Barry Song) | [sched/topology: fix the issue groups don't span domain->span for NUMA diameter > 2](https://lore.kernel.org/patchwork/patch/1371875)| 修复问题 2 | v4 ☑ 5.13-rc1 | [PatchWork](https://lore.kernel.org/patchwork/cover/1371875), [LKML](https://lkml.org/lkml/2021/2/23/1010), [commit](https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=585b6d2723dc927ebc4ad884c4e879e4da8bc21f) |
## 4.2 负载均衡