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[ROCm] Do not use NCCL symmetric buffers on ROCm #46878

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[ROCm] Do not use NCCL symmetric buffers on ROCm #46878

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35 changes: 35 additions & 0 deletions xla/service/gpu/gpu_compiler.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -2504,6 +2504,36 @@ bool RequiresCollectiveOutput(const HloValue* value, const DebugOptions& opts) {
return false;
}

// Symmetric buffers require registering the collective buffers with
// ncclCommWindowRegister(..., NCCL_WIN_COLL_SYMMETRIC). RCCL declares that
// entry point in rccl.h and reports an NCCL version above the one that
// introduced it, so both the build-time and version-based checks pass, but it
// rejects every registration at runtime with ncclInvalidUsage. Enabling
// symmetric buffers therefore fails every multi-device collective on ROCm.
//
// This has to be decided from the device being compiled for, not from a
// build-time define: the defaults are set in
// DefaultDebugOptionsIgnoringFlags(), which is compiled into the
// backend-agnostic jaxlib, while only the plugin and PJRT artifacts are built
// with ROCm configured.
void DisableSymmetricBuffersIfUnsupported(

@sohaibiftikhar sohaibiftikhar Aug 7, 2026

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Shouldn't this be part of amdgpu_compiler?

HloModule* module, const se::DeviceDescription& device_description) {
if (device_description.gpu_compute_capability().rocm_compute_capability() ==
nullptr) {
return;
}
DebugOptions& opts = module->mutable_config().mutable_debug_options();
if (opts.xla_enable_nccl_symmetric_buffers_for_collectives().empty() &&
!opts.xla_gpu_experimental_enable_nccl_symmetric_buffers()) {
return;
}
LOG_FIRST_N(WARNING, 1)
<< "Disabling NCCL symmetric buffers: RCCL does not implement collective "
"window registration (ncclCommWindowRegister).";
opts.clear_xla_enable_nccl_symmetric_buffers_for_collectives();
opts.set_xla_gpu_experimental_enable_nccl_symmetric_buffers(false);
}

void GpuCollectiveBufferAnalysis(
HloModule* module, const HloAliasAnalysis& alias_analysis,
std::function<void(HloInstruction*, const ShapeIndex&)> add_index_to_copy) {
Expand Down Expand Up @@ -2960,6 +2990,11 @@ absl::StatusOr<std::unique_ptr<Executable>> GpuCompiler::RunBackend(
const se::DeviceDescription& gpu_device_info =
gpu_topology.gpu_target_config().device_description;

// Must happen before CompileToBackendResult(): buffer assignment colors
// collective buffers into the collective memory space and thunk emission
// selects the symmetric kernels, both from these debug options.
DisableSymmetricBuffersIfUnsupported(module.get(), gpu_device_info);

if (module->config().hlo_profiling_enabled() || VLOG_IS_ON(1)) {
HloCostAnalysis::Options cost_analysis_options{ShapeSizeBytesFunction()};
cost_analysis_options.set_bytes_per_second(
Expand Down
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