Is softmax scaling optional?

[turboderp]

Can you elaborate on the significance of the softmax scaling? I can't find it referenced in the paper, and it seems to be applied differently for each of the three attention methods in the HF implementation:

• Eager attention applies it whenever the dtype isn't FP32 (since scale_attention_softmax_in_fp32, attention_softmax_in_fp32 and scale_attn_weights are all set.
• SDPA sets a scale of None, though seems prepared to change it to 1 if scale_attn_weights were unset. (?)
• The flash-attn module has provisions for applying the scale in _flash_attention_forward, but that argument isn't passed so it defaults to None.

Presumably the models are trained with flash-attn so is this just not actually relevant?

[Mayank Mishra]

None in SDPA or Flash attention is same as 1 / sqrt(d)
scale_attn_weights is the parameter used to decide whether to use 1 / sqrt(d) or 1 otherwise.
the fp32 arguments is just for stability during training and shouldn't be needed at inference honestly.

[turboderp]

Thank you. 👍