[Mosaic] Add support for specifying estimated costs for Mosaic kernels

PiperOrigin-RevId: 565310871

jax/_src/tpu_custom_call.py

@@ -69,6 +69,19 @@ tpu_custom_call_p.def_impl(
 tpu_custom_call_p.multiple_results = True
 
 
+@dataclasses.dataclass(frozen=True)
+class CostEstimate:
+  flops: int
+  transcendentals: int
+  bytes_accessed: int
+
+  def to_json(self) -> bytes:
+    return (
+        f'{{"flops": {self.flops}, "transcendentals": {self.transcendentals},'
+        f' "bytes_accessed": {self.bytes_accessed}}}'
+    ).encode('ascii')
+
+
 @dataclasses.dataclass(frozen=True)
 class CustomCallBackendConfig:
   """Represents an unserialized backend config for custom calls."""
@@ -76,13 +89,14 @@ class CustomCallBackendConfig:
   has_communication: bool
   collective_id: int | None
   device_type: str | None
+  cost_estimate: CostEstimate | None
 
   # We omit the body while printing, because primitive params get embedded
   # in HLO metadata, and the body blows up its size.
   def __repr__(self):
     return "CustomCallBackendConfig(<omitted>)"
 
-  def to_json(self):
+  def to_json(self) -> bytes:
     """Serializes the backend config into JSON."""
     # We format the JSON ourselves, because json.dumps seems to be overly slow.
     config = io.BytesIO()
@@ -95,6 +109,9 @@ class CustomCallBackendConfig:
     if self.collective_id is not None:
       config.write(b', "collective_id": ')
       config.write(str(self.collective_id).encode("ascii"))
+    if self.cost_estimate is not None:
+      config.write(b', "cost_estimate": ')
+      config.write(self.cost_estimate.to_json())
     config.write(b"}")
     if self.device_type is not None:
       config.write(b', "device_type": ')
@@ -303,6 +320,7 @@ def as_tpu_kernel(
     module: ir.Module,
     out_type: Any,
     *,
+    cost_estimate: CostEstimate | None = None,
     backend: str | xla_client.Client = "tpu",
     device_type: str | None = None,
     kernel_name: str | None = None,
@@ -333,6 +351,7 @@ def as_tpu_kernel(
       has_custom_barrier=has_custom_barrier,
       kernel_name=kernel_name,
       kernel_regeneration_metadata=kernel_regeneration_metadata,
+      cost_estimate=cost_estimate,
   )
 
 
@@ -341,6 +360,7 @@ def _lowered_as_tpu_kernel(
     out_type: Any,
     constants: Sequence[Any] = (),
     *,
+    cost_estimate: CostEstimate | None = None,
     device_type: str | None = None,
     has_communication: bool = False,
     has_custom_barrier: bool = False,
@@ -369,6 +389,7 @@ def _lowered_as_tpu_kernel(
         has_communication,
         collective_id,
         device_type,
+        cost_estimate,
     )
     result = tpu_custom_call_p.bind(
         *args,