Attention-based deep learning models such as the transformers are highly effective in capturing relationship between tokens in an input sequence, even across long distances. As a result, they are used with text, image, and sound-based inputs, where the sequence length can be in thousands of tokens. However, despite the effectiveness of attention modules to capture long term dependencies, in practice, their application to long sequence input is limited by compute and memory requirements of the attention computation that grow quadratically, `O(n^2)`, with the sequence length `n`.
Attention-based deep learning models such as the transformers are highly effective in capturing the relationship between tokens in an input sequence, even across long distances. As a result, they are used with text, image, and sound-based inputs, where the sequence length can be in thousands of tokens. However, despite the effectiveness of attention modules to capture long term dependencies, in practice, their application to long sequence input is limited by compute and memory requirements of the attention computation that grow quadratically, `O(n^2)`, with the sequence length `n`.
To address this limitation, DeepSpeed offers a suite of sparse attention kernels --an instrumental technology that can reduce the compute and memory requirement of attention computation by orders-of-magnitude via block-sparse computation. The suite not only alleviates the memory bottleneck of attention calculation, but also performs sparse computation efficiently. Its APIs allow convenient integration with any transformer-based models. Along with providing a wide spectrum of sparsity structures, it has the flexibility of handling any user-defined block-sparse structures. More specifically, sparse attention (SA) can be designed to compute local attention between nearby tokens, or global attention via summary tokens computed with local attention. Moreover, SA can also allow random attention, or any combination of local, global, and random attention as shown in the following figure with blue, orange, and green blocks, respectively. As a result, SA decreases the memory footprint to `O(wn)`, in which `1 < w < n` is a parameter, whose value depends on the attention structure.
To address this limitation, DeepSpeed offers a suite of sparse attention kernels --an instrumental technology that can reduce the compute and memory requirement of attention computation by orders-of-magnitude via block-sparse computation. The suite not only alleviates the memory bottleneck of attention calculation, but also performs sparse computation efficiently. Its APIs allow convenient integration with any transformer-based models. Along with providing a wide spectrum of sparsity structures, it has the flexibility of handling any user-defined block-sparse structures. More specifically, sparse attention (SA) can be designed to compute local attention between nearby tokens, or global attention via summary tokens computed with local attention. Moreover, SA can also allow random attention, or any combination of local, global, and random attention as shown in the following figure with blue, orange, and green blocks, respectively. As a result, SA decreases the memory footprint to `O(wn)`, in which `1 < w < n` is a parameter, whose value depends on the attention structure.
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@@ -27,7 +27,7 @@ In a pre-training experiment, we ran BERT model under three settings: dense, den
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***up to 6.3x faster computation**
***Up to 6.3x faster computation**
We continued the pre-training experiment for different batch sizes and sequence lengths, using [BERT base/large](https://github.com/microsoft/DeepSpeedExamples/tree/master/bing_bert) and [Megatron GPT2](https://github.com/microsoft/DeepSpeedExamples/tree/master/Megatron-LM). In this experiment we let the training to continue for 100 iteration and recorded the average time per last 30 iterations. SA reduces total computation comparing with dense and improves training speed: the boost is higher with increased sequence length and it is up to 6.3x faster for BERT base, 5.3x for BERT large, and 6.1x for GPT2. Following charts show these results.
We continued the pre-training experiment for different batch sizes and sequence lengths, using [BERT base/large](https://github.com/microsoft/DeepSpeedExamples/tree/master/bing_bert) and [Megatron GPT2](https://github.com/microsoft/DeepSpeedExamples/tree/master/Megatron-LM). In this experiment we let the training to continue for 100 iteration and recorded the average time per last 30 iterations. SA reduces total computation comparing with dense and improves training speed: the boost is higher with increased sequence length and it is up to 6.3x faster for BERT base, 5.3x for BERT large, and 6.1x for GPT2. Following charts show these results.
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@@ -36,14 +36,14 @@ We continued the pre-training experiment for different batch sizes and sequence
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@@ -36,14 +36,14 @@ We continued the pre-training experiment for different batch sizes and sequence
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***higher accuracy**
***Higher accuracy**
Related works along the line of sparse attention ([Sparse Transformer](https://arxiv.org/pdf/1904.10509.pdf), [Longformer](https://arxiv.org/pdf/2004.05150.pdf), [BigBird](https://arxiv.org/pdf/2007.14062.pdf)) have shown comparable or higher accuracy than full attention. Our experience is well aligned. In addition to lower memory overhead and faster computation, we also observe cases in production where SA reaches higher accuracy and faster convergence. The following chart illustrates accuracy of training a production model based on BERT for long document comprehension (2,048 sequence length). The experiment is performed in three settings: dense starting from scratch, SA starting from scratch, and SA continued training from a checkpoint of using dense with sequence length of 512. We have observed that, for pre-training from scratch, SA converges faster with higher accuracy comparing with dense. Furthermore, SA continuing training from a pre-trained checkpoint performs even better, with respect to both time and accuracy.
Related works along the line of sparse attention ([Sparse Transformer](https://arxiv.org/pdf/1904.10509.pdf), [Longformer](https://arxiv.org/pdf/2004.05150.pdf), [BigBird](https://arxiv.org/pdf/2007.14062.pdf)) have shown comparable or higher accuracy than full attention. Our experience is well aligned. In addition to lower memory overhead and faster computation, we also observe cases in production where SA reaches higher accuracy and faster convergence. The following chart illustrates accuracy of training a production model based on BERT for long document comprehension (2,048 sequence length). The experiment is performed in three settings: dense starting from scratch, SA starting from scratch, and SA continued training from a checkpoint of using dense with sequence length of 512. We have observed that, for pre-training from scratch, SA converges faster with higher accuracy comparing with dense. Furthermore, SA continuing training from a pre-trained checkpoint performs even better, with respect to both time and accuracy.
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***comparison with state of the art, Longformer**
***Comparison with state of the art, Longformer**
We compared SA with Longformer, a state-of-the-art sparse structure and implementation. In our experiment, SA uses `Fixed` sparsity, and two implementations have comparable accuracy. On system performance, SA outperforms Longformer both in training and inference:
We compared SA with Longformer, a state-of-the-art sparse structure and implementation. In our experiment, SA uses `Fixed` sparsity, and two implementations have comparable accuracy. On system performance, SA outperforms Longformer both in training and inference:
***1.47x** faster execution pre-training MLM on Wikitext103
***1.47x** faster execution pre-training MLM on Wikitext103
We ran an experiment following the [notebook](https://github.com/allenai/longformer/blob/master/scripts/convert_model_to_long.ipynb) offered by Longformer. In this experiment, we pre-train an MLM model using RoBERTa-base checkpoint. This is done on 8 V100-SXM2 GPU. Following table shows the details of the result in which using DeepSpeed Sparse Attention shows 1.47x speed up.
We ran an experiment following the [notebook](https://github.com/allenai/longformer/blob/master/scripts/convert_model_to_long.ipynb) offered by Longformer. In this experiment, we pre-train an MLM model using RoBERTa-base checkpoint. This is done on 8 V100-SXM2 GPU. Following table shows the details of the result in which using DeepSpeed Sparse Attention shows 1.47x speed up.
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@@ -73,7 +73,7 @@ Through our Long Document Comprehension application we described above, we also
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@@ -73,7 +73,7 @@ Through our Long Document Comprehension application we described above, we also
|32 |1.24 |
|32 |1.24 |
|16 |1.23 |
|16 |1.23 |
***flexibility to handle any block-sparse structure**
***Flexibility to handle any block-sparse structure**
DeepSpeed Sparse Attention suite does not target at any specific sparse structure but enables model scientists to explore any block sparse structure with efficient system support. Currently, we have added popular sparse structure like:
DeepSpeed Sparse Attention suite does not target at any specific sparse structure but enables model scientists to explore any block sparse structure with efficient system support. Currently, we have added popular sparse structure like:
