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Fix garbled output with REPACK at high thread counts #16956

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Merged
merged 3 commits into from
Nov 4, 2025
Merged

Fix garbled output with REPACK at high thread counts #16956

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d746246
Fix garbled output with REPACK at high thread counts
NoahOksuz Nov 2, 2025
fe79c34
Update ggml/src/ggml-cpu/repack.cpp
NoahOksuz Nov 3, 2025
1135d0c
Update ggml/src/ggml-cpu/repack.cpp
NoahOksuz Nov 3, 2025
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25 changes: 25 additions & 0 deletions ggml/src/ggml-cpu/repack.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1678,10 +1678,24 @@ template <typename BLOC_TYPE, int64_t INTER_SIZE, int64_t NB_COLS, ggml_type PAR
int64_t chunk_size = (nr + nth_scaled - 1) / nth_scaled;
int64_t nchunk = (nr + chunk_size - 1) / chunk_size;

// Ensure minimum chunk size to avoid alignment issues with high thread counts
// Minimum chunk size should be at least NB_COLS to prevent overlapping chunks after alignment
const int64_t min_chunk_size = NB_COLS;
if (nchunk > 0 && (nr / nchunk) < min_chunk_size && nr >= min_chunk_size) {
nchunk = (nr + min_chunk_size - 1) / min_chunk_size;
}

if (nth == 1 || nchunk < nth || disable_chunking) {
nchunk = nth;
}

// Ensure nchunk doesn't exceed the number of rows divided by minimum chunk size
// This prevents creating too many tiny chunks that could overlap after alignment
const int64_t max_nchunk = (nr + min_chunk_size - 1) / min_chunk_size;
if (nchunk > max_nchunk) {
nchunk = max_nchunk;
}

if (ith == 0) {
// Every thread starts at ith, so the first unprocessed chunk is nth. This save a bit of coordination right at the start.
ggml_threadpool_chunk_set(params->threadpool, nth);
Expand All @@ -1695,8 +1709,15 @@ template <typename BLOC_TYPE, int64_t INTER_SIZE, int64_t NB_COLS, ggml_type PAR
while (current_chunk < nchunk) {
int64_t src0_start = (current_chunk * ne01) / nchunk;
int64_t src0_end = ((current_chunk + 1) * ne01) / nchunk;

// Align boundaries to NB_COLS - round up to ensure all data is included
// The chunk size limiting above ensures chunks are large enough to prevent overlaps
src0_start = (src0_start % NB_COLS) ? src0_start + NB_COLS - (src0_start % NB_COLS) : src0_start;
src0_end = (src0_end % NB_COLS) ? src0_end + NB_COLS - (src0_end % NB_COLS) : src0_end;
if (src0_end > ne01) {
src0_end = ne01;
}

if (src0_start >= src0_end) {
break;
}
Expand Down Expand Up @@ -1808,8 +1829,12 @@ template <typename BLOC_TYPE, int64_t INTER_SIZE, int64_t NB_COLS, ggml_type PAR
int64_t src0_cur_start = (ith * ne01) / nth;
int64_t src0_cur_end = ((ith + 1) * ne01) / nth;

// Align boundaries to NB_COLS - round up to ensure all data is included
src0_cur_start = (src0_cur_start % NB_COLS) ? src0_cur_start + NB_COLS - (src0_cur_start % NB_COLS) : src0_cur_start;
src0_cur_end = (src0_cur_end % NB_COLS) ? src0_cur_end + NB_COLS - (src0_cur_end % NB_COLS) : src0_cur_end;
if (src0_cur_end > ne01) {
src0_cur_end = ne01;
}

if (src0_cur_start >= src0_cur_end) {
return;
Expand Down
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