V-MoE token droping and MoD

[liyucheng09]

This token dropping method, as indicated by the citation, is based on the V-MoE method.

How this different from the recent MoD? It look like they very similar techniques.

[DeepSeekDDM]

Our token-dropping strategy is just a token-wise dropping w.r.t. the routing probability. It is more like the token-dropping in conventional MoE models like Switch Transformer. It is totally different from MoD, so I do not understand your question. Can you give me more information about your understanding of our token-dropping strategy and MoD? Maybe we can find out something misunderstood.

[Richie-yan]

@DeepSeekDDM @luofuli
Is the capacity in the token-dropping strategy based on the expert dimension or the device dimension?
If it's on the expert dimension, then the capacity is calculated as capacity = math.ceil(num_tokens * topk) / num_experts * capacity_factor, and then each expert processes its own tokens, dropping the least scored tokens if token > capacity, and padding if token < capacity.
If it's on the device dimension, is the capacity calculated as capacity = math.ceil(num_tokens * topk) / num_groups * capacity_factor? How is the token dropping executed in this case?
Because the paper mentions device-level token dropping, I have the above confusion.

[Richie-yan]

Adding another question: How should I understand the statement from the paper that "we ensure that the tokens belonging to approximately 10% of the training sequences will never be dropped"? Is there a specific strategy implemented during token dropping to enforce this?
@DeepSeekDDM @luofuli

[DeepSeekDDM]

@DeepSeekDDM @luofuli Is the capacity in the token-dropping strategy based on the expert dimension or the device dimension? If it's on the expert dimension, then the capacity is calculated as capacity = math.ceil(num_tokens * topk) / num_experts * capacity_factor, and then each expert processes its own tokens, dropping the least scored tokens if token > capacity, and padding if token < capacity. If it's on the device dimension, is the capacity calculated as capacity = math.ceil(num_tokens * topk) / num_groups * capacity_factor? How is the token dropping executed in this case? Because the paper mentions device-level token dropping, I have the above confusion.

A to Q1: Mainly on the device dimension.
A to Q2: Yes.
A to Q3: Also drop tokens with the lowest prob.
A to Q4 & Q5: Yes, we implement a specific strategy to ensure this.

[Richie-yan]

@DeepSeekDDM 确认一下，deepseek v2 实现的是device 维度的drop token
对于 device 维度 去做drop ，是将当前device 所有的expert 分数统一做个排序 然后drop ？

[DeepSeekDDM]

@DeepSeekDDM 确认一下，deepseek v2 实现的是device 维度的drop token 对于 device 维度 去做drop ，是将当前device 所有的expert 分数统一做个排序 然后drop ？

Yes. The actual dropping strategy is a little complex, but the main idea is what you described just now.

[Richie-yan]

@DeepSeekDDM 方便大概讲一下【actual dropping strategy】吗？比较好奇

[DeepSeekDDM]

@DeepSeekDDM 方便大概讲一下【actual dropping strategy】吗？比较好奇

Just some additional tricks to ensure computation efficiency. It is not the key technique of DeepSeekMoE. The details will not prevent you from reproducing DeepSeekMoE.