Add support for sage attention 3 in comfyui, enable via new cli arg #11026
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--use-sage-attiention3
rattus128
reviewed
Dec 2, 2025
| ) | ||
| B, H, L, D = q_s.shape | ||
|
|
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| if dim_head >= 256 or N <= 2048: |
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AFAICT dim_head is undefined if skip_reshape=True
rattus128
reviewed
Dec 2, 2025
| q_s, k_s, v_s = map( | ||
| lambda t: t.view(B, -1, heads, dim_head).permute(0, 2, 1, 3).contiguous(), | ||
| (q, k, v), | ||
| ) |
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You should avoid doing this contiguous until after the below possible fallback, as the below attention_pytorch does not need these reshaped tensors.
rattus128
reviewed
Dec 2, 2025
| try: | ||
| out = sageattn3_blackwell(q_s, k_s, v_s, is_causal=False) | ||
| except Exception as e: | ||
| logging.error("Error running SageAttention3: %s, falling back to pytorch attention.", e) |
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just set a flag here:
do_oom_fallback=True
if do_oom_fallback:
return attention_pytorch(...
The reason is when you catch an exception like this, the exception itself refs all local variables. This means that sage attention local variables including any large tensors are strong reffed by the exception. You want to get out of the except: block before calling attention_pytorch.
del q_s, k_s, v_s before falling back.
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I fixed this in original sage here:
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This is basic Sage Attention 3 support. Because it is still unstable and differs significantly from previous versions of Sage Attention, a separate switch --use-sage-attiention3 is provided to enable or disable it. You need to install Sage Attention 3 in your environment before enabling it.