diff --git a/docs/_tutorials/mixed_precision_zeropp.md b/docs/_tutorials/mixed_precision_zeropp.md new file mode 100644 index 000000000000..12ad3556abde --- /dev/null +++ b/docs/_tutorials/mixed_precision_zeropp.md @@ -0,0 +1,55 @@ +--- +title: "Mixed Precision ZeRO++" +tags: training ZeRO communication-efficiency large-model +--- + +Mixed Precision ZeRO++ (MixZ++) is a set of optimization strategies based on [ZeRO](/tutorials/zero/) and [ZeRO++](/tutorials/zeropp/) to improve the efficiency and reduce memory usage for large model training and inference when users use [Low-Rank Adaptation (LoRA)]([/tutorials/zero/](https://arxiv.org/abs/2106.09685)) training. MixZ++ partitions model parameters across GPUs to reduce footprint and gathers them with quantized communication only when needed similar to its ZeRO and ZeRO++ siblings. Our evaluation indicates MixZ++ increases the training throughput by up to [3.3x](https://github.com/microsoft/DeepSpeed/tree/master/blogs/deepspeed-chat/ds-chat-release-8-31) for the Llama-2-70B model running on 128 V100 GPUs. Read our [DeepSpeed Chat Blog](https://github.com/microsoft/DeepSpeed/tree/master/blogs/deepspeed-chat/ds-chat-release-8-31), [ZeRO++ blog](https://www.microsoft.com/en-us/research/blog/deepspeed-zero-a-leap-in-speed-for-llm-and-chat-model-training-with-4x-less-communication/) and [paper](https://arxiv.org/pdf/2306.10209.pdf) to learn more! + +We recommend that you read the tutorials on [Getting Started](/getting-started/), [ZeRO](/tutorials/zero/) and [Megatron-DeepSpeed](/tutorials/megatron/) before stepping through this tutorial. + +## Key Designs +Mixed Precision ZeRO++ (MixZ++) inherits key designs from [ZeRO++](/tutorials/zeropp/), namely quantized weights (*qwZ*), hierarchical partitioning ZeRO (*hpZ*) but has different applicability: + - *qwZ* applies block-based quantization on frozen weights to reduce memory usage and all-gather communication volume. Compared with ZeRO++, *qwZ* in Mixed Precision ZeRO++ keeps the frozen weights quantized so there is no quantization overhead during runtime and memory usage is reduced. + - *hpZ* eliminates inter-node parameter all-gather communication through data remapping and recomputation. Compared with ZeRO++, *hpZ* in Mixed Precision ZeRO++ applies to both backward and generation passes. + +Collectively, the optimizations bring better scalability and efficiency to LoRA training. Each of the components can be enabled independent of each other and collectively as a group. + +## Enabling Mixed Precision ZeRO++ (MixZ++) + +A ready to go MixZ++ example has been prepared at [MixZ++ example script](https://github.com/microsoft/DeepSpeedExamples/blob/master/applications/DeepSpeed-Chat/training/step3_rlhf_finetuning/training_scripts/llama2/run_llama2_7b_mixz.sh). If you prefer to manually enable MixZ++ in your pipeline, please refer to the instructions below. + +### DeepSpeed Configuration Changes +An example snippet of deepspeed configurations with all MixZ++ optimization enabled is shown below: +```json +{ + "zero_optimization": { + "stage": 3, + "..." + "zero_quantized_nontrainable_weights": true, + "zero_hpz_partition_size": 16, + "..." + } +} +``` +Note that for multi-node training, the `"zero_hpz_partition_size"` should be set to the number of GPUs per node. For example, if you have 8 GPUs per node, then `"zero_hpz_partition_size"` should be set to 8. For single-node training, the `"zero_hpz_partition_size"` should not be set. + +### Training Script Changes +DeepSpeed engine will identify the LoRA frozen parameters if the LoRA model is passed when DeepSpeed initializes. However, the popular implementation is to initialize a base model and then convert to LoRA model later. In such cases, users need to explicitly call DeepSpeed engine after LoRA model is converted. This is only a 1-line effort. An example snippet of training script is shown below: + +```python +model, optimizer, _, lr_scheduler = deepspeed.initialize( + model=model, + optimizer=optimizer, + args=args, + config=ds_config, + lr_scheduler=lr_scheduler, + dist_init_required=True) +# ... +# (the custom code to convert base model to LoRA model) +# ... +# call DeepSpeed engine again to identify LoRA frozen parameters +model.optimizer.quantize_nontrainable_params() +# ... +``` + +Congratulations! You have completed the Mixed Precision ZeRO++ tutorial.