LL128能够以较低的延迟达到较大的带宽率,NCCL会在带有NVLink的机器上默认使用该Protocol 相关代码位于 prims_ll128.h 头文件内 在类初始化的时候,会以每8个thread的最后一个thread作为FlagThread,只有该thread进行Flag位校验: bool flagThread; flagThread((tid%8)==7) 加载数据到寄存器代码为: template<int Wo...
协议:数据构建的协议影响速度,可选的protocol主要是三种,低延时/128B低延时/常规 对应参数:LL/LL128/'Simple。 算法带宽的计算过程:取算法基数值 busBw= ncclTopoGraph->bwIntra ,经过NCCL_ALGO/NCCL_PROTO/NCCL_TOPO等场景修正(即乘以一定的比例系数)后,把结果存储在comm中: 参数含义:coll: 集群通信操作;a:...
NCCL 2.6 引入了一种创新的通信算法——CollNet算法,它是建立在SHArP(Scalable Hierarchical Aggregation and Reduction Protocol)基础之上的,专为与InfiniBand(IB)网络配合使用而设计。 SHArP,也被称为NCCL Plugin或NCCL-RDMA-SHARP插件,是提升通信性能的关键工具,它通过优化数据在网络中的传输方式,显著提高了大规模GPU...
一般来说更在乎latency的会选择LL,更在乎带宽的会选择Simple,至于LL128,可能只在特定的硬件架构上能支持,用到的情况可能不是很多。关于proto的解释可见What is LL128 Protocol? · Issue #281 · NVIDIA/nccl 实际上NCCL会选择什么Algo + proto的组合是NCCL自己来决定的,当然我们也可以通过NCCL_ALGO 和 NCCL_PROT...
LL/LL128/'Simple:NCCL格式协议 低延时/128B低延时/常规。LL表示数据携带一般flag标记:4B data / 4 B flag;LL128表示128B 存储:120B data / 8 B flag。参看:What is LL128 Protocol? · Issue #281 · NVIDIA/nccl 参考资料: GitHub - NVIDIA/nccl: Optimized primitives for collective multi-GPU commu...
Supported subsystem names are INIT (stands for initialization), COLL (stands for collectives), P2P (stands for peer-to-peer), SHM (stands for shared memory), NET (stands for network), GRAPH (stands for topology detection and graph search), TUNING (stands for algorithm/protocol tuning), ENV...
NCCL会构建 tree,ring graph。 Tree Logical Topology log 10.0.2.11:2be7fa6883db:57976:58906[5]NCCLINFOTrees[0]14/-1/-1->13->12[1]14/-1/-1->13->1210.0.2.11:2be7fa6883db:57977:58920[6]NCCLINFOTrees[0]15/-1/-1->14->13[1]15/-1/-1->14->1310.0.2.11:2be7fa6883db:57978:5891...
Update performance tuning for recent Intel CPUs * Improve algorithm/protocol selection on recent CPUs such as Emerald Rapids and Sapphire Rapids. Improve channel scheduling when mixing LL and Simple operations. * Make LL operations account for 4x more traffic to ensure LL and simple operations ...
NCCL会构建tree，ring graph。依此解析，可得两棵一样的tree，逻辑拓扑如下：其中socket双工通道建立如下(双工为1个channel)：依此解析，可得两个一样的ring，逻辑拓扑如下：用户调用NCCL支持的集合通信原语进行通信：NCCL在getAlgoInfo里面使用ncclTopoGetAlgoTime来计算每个(algorithm, protocol)组，最终选择...
I'm working on distributed AI/ML training. I have 2 machines each have 1 GPU and 2 RNICS. I'm using horovod with nccl, in this case i have noticed that rdma write stats are getting updated whereas if i use horovod with mpi i have noticed rdma read stats are getting updated. can ...