Source code for maxtext.kernels.megablox.common

# Copyright 2023–2026 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
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#    https://www.apache.org/licenses/LICENSE-2.0
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"""Common utilities for GMM kernels."""

import re

import jax
import jax.numpy as jnp




def is_tpu() -> bool:
  return "TPU" in jax.devices()[0].device_kind





def tpu_kind() -> str:
  """Query identification string for the currently attached TPU."""
  return jax.devices()[0].device_kind



# Ex: VPU v5; TPU v5 lite; TPU7x
_TPU_KIND_PATTERN = re.compile(r"TPU(?: v)?(\d+)")




def tpu_generation() -> int:
  """Generation number of the currently attached TPU."""
  my_tpu_kind = tpu_kind()
  if version := _TPU_KIND_PATTERN.match(my_tpu_kind):
    return int(version[1])
  raise NotImplementedError(f"Only TPU devices are supported: Invalid device_kind: '{my_tpu_kind}'")





def supports_bfloat16_matmul() -> bool:
  """Does the currently attached CPU support bfloat16 inputs?"""
  return not is_tpu() or tpu_generation() >= 4





def assert_is_supported_dtype(dtype: jnp.dtype) -> None:
  if dtype not in (jnp.bfloat16, jnp.float32):
    raise ValueError(f"Expected bfloat16 or float32 array but got {dtype}.")





def select_input_dtype(lhs: jnp.ndarray, rhs: jnp.ndarray) -> jnp.dtype:
  """A type to which both input should be adapted to before dot product."""
  # bf16xbf16 matmul is only supported since TPUv4 generation. In case of mixed
  # input precision, we need to convert bf16 argument to fp32 beforehand.
  if supports_bfloat16_matmul() and lhs.dtype == jnp.bfloat16 and rhs.dtype == jnp.bfloat16:
    return jnp.bfloat16
  else:
    return jnp.float32