collamark
Mark the best lines
Install CollaMark
精英們對宗教機構的成員和結構行使統治權
指導和應用作用的現象
本地拓扑检测主要是对comm→topo参数的填充,再通过它来搜索找到带宽最大化的路径,形成本地环路
拓扑探测流程实现在initTransportsRank函数中
这种环路复制的方法显著提升了数据传输的并行度,从而增强了整体的通信效率。
通信库会根据机器的PCI、QPI、网卡等硬件的带宽特性,探测并建立多条环路。例如在多机环境下,服务器节点中有多少个网卡,通信库就会依次使用不同的本地网卡作为环路的起始节点进行探测,一般情况下会形成与网卡数量一致的环路数量。
环路的首尾节点通常都是一张网卡
managing multiple GPUs from one thread (to avoid deadlocks), aggregating communication operations to improve performance, or merging multiple send/receive point-to-point operations
Each CUDA device is identified within the communication group by a zero-based index or rank. Each rank uses a communicator object to refer to the collection of GPUs that are intended to work together.
NCCL collectives take a “stream” argument which provides direct integration with the CUDA programming model.
NCCL provides fast collectives over multiple GPUs both within and across nodes. It supports a variety of interconnect technologies including PCIe, NVLINK, InfiniBand Verbs, and IP sockets.
CUDA based collectives would traditionally be realized through a combination of CUDA memory copy operations and CUDA kernels for local reductions. NCCL, on the other hand, implements each collective in a single kernel handling both communication and computation operations.
Tight synchronization
point-to-point send/receive communication which allows for scatter, gather, or all-to-all operations
The NVIDIA Collective Communications Library (NCCL, pronounced “Nickel”) is a library providing inter-GPU communication primitives that are topology-aware and can be easily integrated into applications
collective communication primitives : AllReduce Broadcast Reduce AllGather ReduceScatter
T1的构建方式下边会介绍,T2的构造有两种方式,一种是shift,将rank向左shift一位,比如rank10变成rank9,然后通过和T1一样的方式构造,这种构造方式下T1和T2的树结构完全一致;另外一种是mirror,将rank号镜像一下,比如rank0镜像为rank9,这种构造方式下T1和T2树结构是镜像对称的,不过mirror的方式只能用于机器数为偶数的场景,否则会存在节点在两棵树中都是叶节点。
前缀和
节点间通信:Tree 算法适用于节点间的网络通信环境,能够减少延迟并具有良好的扩展性。
节点内通信:Ring 算法适用于节点内的高速互联环境,能够高效利用带宽和拓扑结构。 节点间通信:Tree 算法适用于节点间的网络通信环境,能够减少延迟并具有良好的扩展性。
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