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Use load_vector in arg_reduce #2439

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Merged
merged 1 commit into from
Jul 30, 2025
Merged

Use load_vector in arg_reduce #2439

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19 changes: 12 additions & 7 deletions mlx/backend/cuda/arg_reduce.cu
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Original file line number Diff line number Diff line change
Expand Up @@ -44,8 +44,11 @@ struct ArgMin {
}

template <int N>
__device__ IndexValPair<T>
reduce_many(IndexValPair<T> best, T (&vals)[N], uint32_t offset) {
__device__ IndexValPair<T> reduce_many(
IndexValPair<T> best,
const AlignedVector<T, N>& vals,
uint32_t offset) {
#pragma unroll
for (int i = 0; i < N; i++) {
if (vals[i] < best.val) {
best.val = vals[i];
Expand Down Expand Up @@ -74,8 +77,11 @@ struct ArgMax {
}

template <int N>
__device__ IndexValPair<T>
reduce_many(IndexValPair<T> best, T (&vals)[N], uint32_t offset) {
__device__ IndexValPair<T> reduce_many(
IndexValPair<T> best,
const AlignedVector<T, N>& vals,
uint32_t offset) {
#pragma unroll
for (int i = 0; i < N; i++) {
if (vals[i] > best.val) {
best.val = vals[i];
Expand Down Expand Up @@ -106,16 +112,15 @@ __global__ void arg_reduce_general(

int64_t in_idx = elem_to_loc(index, shape.data(), in_strides.data(), ndim);
int64_t out_idx = elem_to_loc(index, shape.data(), out_strides.data(), ndim);
in += in_idx;

Op op;
T init = op.init();
IndexValPair<T> best{0, init};

for (int r = 0; r < cuda::ceil_div(axis_size, BLOCK_DIM * N_READS); ++r) {
T vals[N_READS];
auto tid = r * BLOCK_DIM + block.thread_index().x;
cub::LoadDirectBlocked(
tid, StridedIterator(in + in_idx, axis_stride), vals, axis_size, init);
auto vals = load_vector<N_READS>(in, tid, axis_size, axis_stride, init);
best = op.reduce_many(best, vals, tid * N_READS);
}

Expand Down
14 changes: 0 additions & 14 deletions mlx/backend/cuda/device/utils.cuh
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Expand Up @@ -131,20 +131,6 @@ inline __device__ void store_vector(
}
}

// Helper for accessing strided data.
template <typename T>
struct StridedIterator {
T it;
int64_t stride;

__host__ __device__ StridedIterator(T it, int64_t stride)
: it(it), stride(stride) {}

__host__ __device__ auto operator[](int i) const {
return it[i * stride];
}
};

///////////////////////////////////////////////////////////////////////////////
// Type limits utils
///////////////////////////////////////////////////////////////////////////////
Expand Down