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[HIP] [Bugfix] Skip empty inputs in custom all-gather #7302

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Merged
TennyWang1223 merged 1 commit into from
Nov 4, 2026
Merged

[HIP] [Bugfix] Skip empty inputs in custom all-gather #7302

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6 changes: 6 additions & 0 deletions csrc/include/custom_all_reduce.cuh
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Original file line number Diff line number Diff line change
Expand Up @@ -5130,6 +5130,12 @@ template <typename T>
void dispatchAllGather(
hipStream_t stream, T* input, T* output, int size, int last_dim_size, int gather_dim)
{
// Idle DP-attention groups can have empty shards. There is no payload to exchange,
// and launching zero blocks would leave an error for the next operator to report.
if(size == 0)
{
return;
}
RankData* ptrs = get_buffer_RD(stream, input);
auto d = 16 / sizeof(T);
dim3 block(512);
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7 changes: 5 additions & 2 deletions csrc/kernels/custom_all_reduce.cu
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Expand Up @@ -521,8 +521,11 @@ void all_gather_unreg(fptr_t _fa,

if(data_bytes > reg_bytes)
throw std::runtime_error("registered buffer is too small to contain the input");
HIP_CALL(hipMemcpyAsync((void*)reg_buffer, inp.data_ptr(), data_bytes,
hipMemcpyDeviceToDevice, stream));
if(data_bytes != 0)
{
HIP_CALL(hipMemcpyAsync(
(void*)reg_buffer, inp.data_ptr(), data_bytes, hipMemcpyDeviceToDevice, stream));
}
_all_gather(_fa, (void*)reg_buffer, out.data_ptr(), inp.numel(), inp.dtype(),
last_dim_size, dim);
}
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