NCCL VS xla

% rm -rf /tmp/nccl ; git clone --recursive https://github.com/NVIDIA/nccl.git ; cd nccl ; git grep MPI Cloning into 'nccl'... remote: Enumerating objects: 2769, done. remote: Counting objects: 100% (336/336), done. remote: Compressing objects: 100% (140/140), done. remote: Total 2769 (delta 201), reused 287 (delta 196), pack-reused 2433 Receiving objects: 100% (2769/2769), 3.04 MiB | 3.37 MiB/s, done. Resolving deltas: 100% (1820/1820), done. README.md:NCCL (pronounced "Nickel") is a stand-alone library of standard communication routines for GPUs, implementing all-reduce, all-gather, reduce, broadcast, reduce-scatter, as well as any send/receive based communication pattern. It has been optimized to achieve high bandwidth on platforms using PCIe, NVLink, NVswitch, as well as networking using InfiniBand Verbs or TCP/IP sockets. NCCL supports an arbitrary number of GPUs installed in a single node or across multiple nodes, and can be used in either single- or multi-process (e.g., MPI) applications. src/collectives/broadcast.cc:/* Deprecated original "in place" function, similar to MPI */

If it's rendering, you don't really need SLI, you need to install NCCL so that GPUs memory can be pooled: https://github.com/NVIDIA/nccl

backends from native torch distributed configuration: nccl, gloo, mpi.

> The PyTorch/XLA Team at Google

Meanwhile you have an issue from 5 years ago with 0 support

https://github.com/pytorch/xla/issues/202

PyTorch has had an XLA backend for years. I don't know how performant it is though. https://pytorch.org/xla

It's curtains for XLA, to be precise. And PyTorch officially supports XLA backend nowadays too ([1]), which kind of makes JAX and PyTorch standing on the same foundation.

1. https://github.com/pytorch/xla

Pytorch supports other kinds of accelerators (e.g. FPGA, and https://github.com/pytorch/glow), but unless you want to become a ML systems engineer and have money and time to throw away, or a business case to fund it, it is not worth it. In general, both pytorch and tensorflow have hardware abstractions that will compile down to device code. (XLA, https://github.com/pytorch/xla, https://github.com/pytorch/glow). TPUs and GPUs have very different strengths; so getting top performance requires a lot of manual optimizations. Considering the the cost of training LLM, it is time well spent.

While apparently TPUs can theoretically achieve great speedups, getting to the point where they beat a single GPU requires a lot of fiddling around and debugging. A specific setup is required to make it work properly. E.g., here it says that to exploit TPUs you might need a better CPU to keep the TPU busy, than the one in colab. The tutorials I looked at oversimplified the whole matter, the same goes for pytorch-lightning which implies switching to TPU is as easy as changing a single parameter. Furthermore, none of the tutorials I saw (even after specifically searching for that) went into detail about why and how to set up a GCS bucket for data loading.

XLA on TPUs via pytorch/xla.

I don't know of any such trick except for using TensorFlow. In fact, I benchmarked PyTorch XLA vs TensorFlow and found that the former's performance was quite abysmal: PyTorch XLA is very slow on Google Colab. The developers' explanation, as I understood it, was that TF was using features not available to the PyTorch XLA developers and that they therefore could not compete on performance. The situation may be different today, I don't know really.