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[OUTDATED] perf: optimize fused AllReduce + RMSNorm (custom_all_reduce) #3462

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[OUTDATED] perf: optimize fused AllReduce + RMSNorm (custom_all_reduce) #3462

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ab22026
perf: ar add dpp fast path
ftyghome Jun 1, 2026
80fd821
perf(custom_all_reduce): FLAT reduce-scatter stage1 + decode win-gate…
ftyghome Jun 8, 2026
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25 changes: 24 additions & 1 deletion csrc/include/custom_all_reduce.cuh
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Original file line number Diff line number Diff line change
Expand Up @@ -908,9 +908,32 @@ template<typename T>
DINLINE T shfl_xor(T var, int mask, int width = opus::get_warp_size())
{
static_assert(sizeof(T) == 4);
int v = __builtin_bit_cast(int, var);
switch(mask)
{
case 1:
return __builtin_bit_cast(T, __builtin_amdgcn_mov_dpp(v, 0xb1, 0xf, 0xf, true));
case 2:
return __builtin_bit_cast(T, __builtin_amdgcn_mov_dpp(v, 0x4e, 0xf, 0xf, true));
case 4:
{
int r = __builtin_amdgcn_update_dpp(v, v, 0x104, 0xf, 0x5, true);
r = __builtin_amdgcn_update_dpp(r, v, 0x114, 0xf, 0xa, true);
Comment on lines +915 to +921
return __builtin_bit_cast(T, r);
}
case 8:
{
int r = __builtin_amdgcn_update_dpp(v, v, 0x108, 0xf, 0x3, true);
r = __builtin_amdgcn_update_dpp(r, v, 0x118, 0xf, 0xc, true);
Comment on lines +926 to +927
return __builtin_bit_cast(T, r);
}
Comment on lines +912 to +929
default:
break;
}
// fallback
int self = opus::lane_id();
int index = (self & ~(width - 1)) + ((self ^ mask) & (width - 1));
return __builtin_bit_cast(T, __builtin_amdgcn_ds_bpermute(index << 2, __builtin_bit_cast(int, var)));
return __builtin_bit_cast(T, __builtin_amdgcn_ds_bpermute(index << 2, v));
}

// shfl_xor support 4bytes dtype only
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