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Pass input_output_alias to TritonAutotunedKernelCall #2814

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Merged
tdophung merged 3 commits into from
Apr 2, 2026
Merged

Pass input_output_alias to TritonAutotunedKernelCall #2814

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918df1e
Pass input_output_alias to TritonAutotunedKernelCall
nvjax Mar 31, 2026
7ed5f95
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Mar 31, 2026
f4e7f52
Add jax version guard for the input_output_aliasing fix
tdophung Mar 31, 2026
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38 changes: 24 additions & 14 deletions transformer_engine/jax/triton_extensions/utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -43,8 +43,10 @@
import jax.numpy as jnp

from ..version_utils import (
TRITON_AUTOTUNED_INPUT_OUTPUT_ALIAS_MIN_JAX_VERSION,
TRITON_EXTENSION_MIN_JAX_VERSION,
is_triton_extension_supported,
jax_version_meet_requirement,
)


Expand Down Expand Up @@ -474,23 +476,31 @@ def lowering(ctx, x, *, block_size):

kernel_calls.append((config_call, str(config)))

# IMPORTANT: We pass an empty tuple for input_output_aliases_with_sizes.
#
# Background:
# 1. jax.ffi.ffi_lowering(operand_output_aliases=...) is a HINT to XLA that an
# output can reuse an input's buffer. XLA may or may not honor this.
# 2. TritonAutotunedKernelCall's input_output_aliases_with_sizes triggers
# save/restore logic during autotuning (see jaxlib/gpu/triton_kernels.cc:630-701).
#
# The problem: The save phase (triton_kernels.cc:632) only saves if buffers[input_idx] == buffers[output_idx],
# but the restore phase (triton_kernels.cc:697-700) unconditionally iterates over all aliases and tries
# to access input_copies[input_idx]. If XLA didn't actually alias the buffers, input_copies[input_idx] doesn't exist, creating an empty vector whose .data() returns nullptr, causing CUDA_ERROR_INVALID_VALUE during the restore memcpy.
#
# WAR: Don't pass aliases to TritonAutotunedKernelCall.
input_output_aliases_with_sizes = ()
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if input_output_aliases:
if jax_version_meet_requirement(TRITON_AUTOTUNED_INPUT_OUTPUT_ALIAS_MIN_JAX_VERSION):
num_inputs = len(ctx.avals_in)
aliases = []
for input_idx, output_idx in input_output_aliases.items():
aval = ctx.avals_in[input_idx]
size_bytes = aval.size * jnp.dtype(aval.dtype).itemsize
# AutotunedKernelCall expects buffer indices (inputs + outputs).
buffer_output_idx = num_inputs + output_idx
aliases.append((input_idx, buffer_output_idx, size_bytes))
input_output_aliases_with_sizes = tuple(aliases)
else:
warnings.warn(
f"JAX >= {TRITON_AUTOTUNED_INPUT_OUTPUT_ALIAS_MIN_JAX_VERSION} is required "
"to safely pass input_output_aliases to TritonAutotunedKernelCall. "
"Passing empty aliases as a workaround (jax-ml/jax#35218).",
UserWarning,
stacklevel=2,
)

kernel_call = gpu_triton.TritonAutotunedKernelCall(
f"{actual_kernel_fn.__name__}_autotuned",
kernel_calls,
(), # Empty to avoid buggy save/restore in jaxlib/gpu/triton_kernels.cc
input_output_aliases_with_sizes,
)

else:
Expand Down
10 changes: 10 additions & 0 deletions transformer_engine/jax/version_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -25,6 +25,15 @@ def jax_version_meet_requirement(version: str):
# Minimum JAX version required for Triton kernel dispatch (jaxlib < 0.8.0 segfaults).
TRITON_EXTENSION_MIN_JAX_VERSION = "0.8.0"

# Minimum JAX version for safe input_output_aliases in TritonAutotunedKernelCall.
# jaxlib/gpu/triton_kernels.cc had a bug in the autotuning save/restore loop:
# it iterated over all declared aliases unconditionally, but input_copies only
# contains entries for aliases where XLA actually shared buffers at runtime.
# Accessing a missing entry produced a null vector → CUDA_ERROR_INVALID_VALUE.
# Fixed by: https://github.com/jax-ml/jax/pull/35218 (merged 2026-03-17, main).
# Ships in JAX 0.9.3 (not yet released as of 2026-03-31).
TRITON_AUTOTUNED_INPUT_OUTPUT_ALIAS_MIN_JAX_VERSION = "0.9.3"


def is_triton_extension_supported() -> bool:
"""Return True if the current JAX version supports Triton kernel dispatch.
Expand All @@ -40,4 +49,5 @@ def is_triton_extension_supported() -> bool:
"jax_version_meet_requirement",
"is_triton_extension_supported",
"TRITON_EXTENSION_MIN_JAX_VERSION",
"TRITON_AUTOTUNED_INPUT_OUTPUT_ALIAS_MIN_JAX_VERSION",
]
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