Expose sa_fuse_reciprocal and sa_use_base2_exp flags in MaxText

This change exposes two flags that are supported by the underlying tokamax SplashConfig:
- sa_fuse_reciprocal: Maps to fuse_reciprocal in SplashConfig (defaults to True).
- sa_use_base2_exp: Maps to use_base2_exp in SplashConfig (defaults to True).

These are passed to tokamax_splash_kernel.SplashConfig.

TAG=agy
CONV=9b0f857c-78d2-4359-be96-73df07e21957
CHANGE_STEWARD=true

Author: dandragona

src/maxtext/configs/base.yml

@@ -1101,6 +1101,8 @@ sa_q_layout: "HEAD_DIM_MINOR"
 sa_k_layout: "HEAD_DIM_MINOR"
 sa_v_layout: "HEAD_DIM_MINOR"
 use_splash_scheduler: false # to use tokamax splash attention scheduler.
+sa_fuse_reciprocal: true # defaults to true in Tokamax
+sa_use_base2_exp: true # defaults to true in Tokamax
 # local_sa_* variants apply to local (sliding window) attention layers;
 # if None, each inherits from the corresponding global sa_* flag.
 local_sa_block_q: None  # inherits from sa_block_q if None
@@ -1116,6 +1118,8 @@ local_sa_q_layout: None  # inherits from sa_q_layout if None
 local_sa_k_layout: None  # inherits from sa_k_layout if None
 local_sa_v_layout: None  # inherits from sa_v_layout if None
 local_use_splash_scheduler: None  # inherits from use_splash_scheduler if None
+local_sa_fuse_reciprocal: None  # inherits from sa_fuse_reciprocal if None
+local_sa_use_base2_exp: None  # inherits from sa_use_base2_exp if None
 use_max_logit_estimate: -1 # -1 means no estimate, any > 0 value will be used as max logit estimate
 cost_estimate_flops_fwd: -1 # -1 means using splash default cost estmiation, any >= 0 value will be used as cost estmiation for splash to overlap for communication (forward)
 cost_estimate_flops_bwd: -1 # -1 means using splash default cost estmiation, any >= 0 value will be used as cost estmiation for splash to overlap for communication (backward)

src/maxtext/configs/types.py

@@ -700,6 +700,8 @@ class SplashAttention(BaseModel):
   sa_k_layout: str = Field("HEAD_DIM_MINOR", description="Layout for K in splash attention.")
   sa_v_layout: str = Field("HEAD_DIM_MINOR", description="Layout for V in splash attention.")
   use_splash_scheduler: bool = Field(False, description="Use experimental splash attention scheduler.")
+  sa_fuse_reciprocal: bool = Field(True, description="Maps to fuse_reciprocal in SplashConfig.")
+  sa_use_base2_exp: bool = Field(True, description="Maps to use_base2_exp in SplashConfig.")
   # If None, each local_sa_* flag inherits from the corresponding sa_* flag.
   local_sa_block_q: int | None = Field(None, description="Block size for Q in local splash attention.")
   local_sa_block_kv: int | None = Field(None, description="Block size for KV in local splash attention.")
@@ -718,6 +720,8 @@ class SplashAttention(BaseModel):
   local_sa_k_layout: str | None = Field(None, description="Layout for K in local splash attention.")
   local_sa_v_layout: str | None = Field(None, description="Layout for V in local splash attention.")
   local_use_splash_scheduler: bool | None = Field(None, description="Use experimental local splash attention scheduler.")
+  local_sa_fuse_reciprocal: bool | None = Field(None, description="Maps to local fuse_reciprocal in SplashConfig.")
+  local_sa_use_base2_exp: bool | None = Field(None, description="Maps to local use_base2_exp in SplashConfig.")
   use_max_logit_estimate: int = Field(
       -1,
       description="-1 means no estimate, any > 0 value will be used as max logit estimate",
@@ -2984,6 +2988,10 @@ def calculate_global_batch_sizes(per_device_batch_size, expansion_factor, num_de
       self.local_sa_v_layout = self.sa_v_layout
     if self.local_use_splash_scheduler is None:
       self.local_use_splash_scheduler = self.use_splash_scheduler
+    if self.local_sa_fuse_reciprocal is None:
+      self.local_sa_fuse_reciprocal = self.sa_fuse_reciprocal
+    if self.local_sa_use_base2_exp is None:
+      self.local_sa_use_base2_exp = self.sa_use_base2_exp
 
     # I. RUN ALL CROSS-FIELD VALIDATIONS
     if self.load_parameters_path and self.load_full_state_path:

src/maxtext/layers/attention_op.py

@@ -495,6 +495,8 @@ def __init__(
         self.k_layout = self.config.local_sa_k_layout
         self.v_layout = self.config.local_sa_v_layout
         self.use_splash_scheduler = self.config.local_use_splash_scheduler
+        self.fuse_reciprocal = self.config.local_sa_fuse_reciprocal
+        self.use_base2_exp = self.config.local_sa_use_base2_exp
       else:
         self.block_q = self.config.sa_block_q
         self.block_kv = self.config.sa_block_kv
@@ -509,6 +511,8 @@ def __init__(
         self.k_layout = self.config.sa_k_layout
         self.v_layout = self.config.sa_v_layout
         self.use_splash_scheduler = self.config.use_splash_scheduler
+        self.fuse_reciprocal = self.config.sa_fuse_reciprocal
+        self.use_base2_exp = self.config.sa_use_base2_exp
     self.attn_logits_soft_cap = attn_logits_soft_cap
     self.sliding_window_size = sliding_window_size
     self.chunk_attn_window_size = chunk_attn_window_size
@@ -1226,6 +1230,8 @@ def create_sa_config(config, query, key, attn_logits_soft_cap):
             k_layout=tokamax_splash_kernel.QKVLayout[self.k_layout],
             v_layout=tokamax_splash_kernel.QKVLayout[self.v_layout],
             attn_logits_soft_cap=attn_logits_soft_cap,
+            fuse_reciprocal=self.fuse_reciprocal,
+            use_base2_exp=self.use_base2_exp,
             residual_checkpoint_name="context",
             fwd_cost_estimate=pl.CostEstimate(
                 flops=config.cost_estimate_flops_fwd,