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fix: enable ulysses sharding for custom kernels and improve scaling precision #396

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copybara-service merged 1 commit into from
May 4, 2026
+4 −5
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fix: enable ulysses sharding for custom kernels and improve scaling precision #396

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7 changes: 3 additions & 4 deletions src/maxdiffusion/models/attention_flax.py
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,7 @@
from . import quantizations
from .modeling_flax_utils import get_activation

LOG2E = math.log2(math.e)

Array = common_types.Array
Mesh = common_types.Mesh
Expand Down Expand Up @@ -591,9 +592,7 @@ def wrap_ulysses_attention(query, key, value):
heads_per_tile = getattr(flash_block_sizes, "heads_per_tile", heads_per_tile)

if use_base2_exp:
query_scaled = query * 1.44269504
else:
query_scaled = query
query = query * LOG2E

query, kv_size, query_seq_len = _pad_data_for_flash(query, heads, bq)
key, _, key_seq_len = _pad_data_for_flash(key, heads, bkv)
Expand All @@ -612,7 +611,7 @@ def wrap_ulysses_attention(query, key, value):
)

vmapped_splash = jax.vmap(splash_kernel, in_axes=(0, 0, 0))
attention_output = vmapped_splash(query_scaled, key, value)
attention_output = vmapped_splash(query, key, value)
attention_output = jnp.swapaxes(attention_output, 2, 3)
attention_output = attention_output[:, :, :query_seq_len, :kv_size].astype(query.dtype)
else:
Expand Down
2 changes: 1 addition & 1 deletion src/maxdiffusion/pyconfig.py
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Expand Up @@ -214,7 +214,7 @@ def user_init(raw_keys):
# Verify qkv is sharded across sequence.
attention = raw_keys["attention"]
uses_ring_attention = "ring" in attention
uses_ulysses_attention = attention == "ulysses"
uses_ulysses_attention = "ulysses" in attention
uses_uniform_sequence_sharding = raw_keys["attention_sharding_uniform"]
if uses_ring_attention or uses_ulysses_attention or uses_uniform_sequence_sharding:
max_logging.log(
Expand Down
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