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[SYCL] Fix reorder MMVQ assert on unaligned vocab sizes (#22035)

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* [SYCL] Fix reorder MMVQ assert on unaligned vocab sizes

The reorder mul_mat_vec_q dispatchers for Q4_0, Q8_0, Q4_K, and Q6_K
asserted that block_num_y was a multiple of 16 subgroups. Models with
a vocab size not divisible by 16 (for example HY-MT at 120818) aborted
on model load when the output projection tripped the assert.

I replaced the assert with padding: block_num_y now rounds up to a
whole number of subgroup-sized workgroups. The kernel already has the
row bounds check (`if (row >= nrows) return;`) so the extra padded
threads early-exit cleanly. Row values are uniform across a subgroup
so the collective reduce stays safe.

For aligned vocab sizes the padded block_num_y equals the old value,
so the kernel launch is identical and there is no regression.

Thanks to @arthw for flagging the relationship to #21527.

Fixes #22020.

AI assisted coding, tested on Intel B70 hardware.

* sycl: use WARP_SIZE for num_subgroups in reorder MMVQ launches

Replaces the hardcoded 16 with WARP_SIZE in the four reorder_mul_mat_vec
launch helpers (Q4_0, Q8_0, Q4_K, Q6_K). Compile-time no-op on the Intel
target where WARP_SIZE is 16, but makes the relationship to subgroup
size explicit. Per review by @NeoZhangJianyu on #22035.

Assisted by Claude.
This commit is contained in:
Katostrofik 2026-04-20 01:39:45 -04:00 committed by GitHub
parent 9d49acb2a7
commit 788fcbc5dd
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1 changed files with 12 additions and 12 deletions
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24
ggml/src/ggml-sycl/mmvq.cpp
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@ -537,9 +537,9 @@ static void mul_mat_vec_q_iq4_xs_q8_1(const void *__restrict__ vx,
static void reorder_mul_mat_vec_q4_0_q8_1_sycl(const void * vx, const void * vy, float * dst, const int ncols,
const int nrows, dpct::queue_ptr stream) {
GGML_ASSERT(ncols % QK4_0 == 0);
const int block_num_y = ceil_div(nrows, GGML_SYCL_MMV_Y);
constexpr size_t num_subgroups = 16;
GGML_ASSERT(block_num_y % num_subgroups == 0);
// Round up to a whole number of subgroup-sized workgroups; out-of-range rows are skipped inside the kernel.
constexpr size_t num_subgroups = WARP_SIZE;
const int block_num_y = ceil_div(nrows, GGML_SYCL_MMV_Y * (int) num_subgroups) * (int) num_subgroups;
const sycl::range<3> global_size(1, GGML_SYCL_MMV_Y, (block_num_y * WARP_SIZE));
const sycl::range<3> workgroup_size(1, GGML_SYCL_MMV_Y, num_subgroups * WARP_SIZE);
@ -682,9 +682,9 @@ static void mul_mat_vec_q5_1_q8_1_sycl(const void *vx, const void *vy,
static void reorder_mul_mat_vec_q8_0_q8_1_sycl(const void * vx, const void * vy, float * dst, const int ncols,
const int nrows, dpct::queue_ptr stream) {
GGML_ASSERT(ncols % QK8_0 == 0);
const int block_num_y = ceil_div(nrows, GGML_SYCL_MMV_Y);
constexpr size_t num_subgroups = 16;
GGML_ASSERT(block_num_y % num_subgroups == 0);
// Round up to a whole number of subgroup-sized workgroups; out-of-range rows are skipped inside the kernel.
constexpr size_t num_subgroups = WARP_SIZE;
const int block_num_y = ceil_div(nrows, GGML_SYCL_MMV_Y * (int) num_subgroups) * (int) num_subgroups;
const sycl::range<3> global_size(1, GGML_SYCL_MMV_Y, (block_num_y * WARP_SIZE));
const sycl::range<3> workgroup_size(1, GGML_SYCL_MMV_Y, num_subgroups * WARP_SIZE);
@ -798,9 +798,9 @@ static void reorder_mul_mat_vec_q4_k_q8_1_sycl(const void * vx, const void * vy,
const int nrows, dpct::queue_ptr stream) {
GGML_ASSERT(ncols % QK_K == 0);
const int block_num_y = ceil_div(nrows, GGML_SYCL_MMV_Y);
constexpr size_t num_subgroups = 16;
GGML_ASSERT(block_num_y % num_subgroups == 0);
// Round up to a whole number of subgroup-sized workgroups; out-of-range rows are skipped inside the kernel.
constexpr size_t num_subgroups = WARP_SIZE;
const int block_num_y = ceil_div(nrows, GGML_SYCL_MMV_Y * (int) num_subgroups) * (int) num_subgroups;
const sycl::range<3> global_size(1, GGML_SYCL_MMV_Y, block_num_y * WARP_SIZE);
const sycl::range<3> workgroup_size(1, GGML_SYCL_MMV_Y, num_subgroups * WARP_SIZE);
@ -842,9 +842,9 @@ static void mul_mat_vec_q5_K_q8_1_sycl(const void *vx, const void *vy,
static void reorder_mul_mat_vec_q6_k_q8_1_sycl(const void * vx, const void * vy, float * dst, const int ncols,
const int nrows, dpct::queue_ptr stream) {
GGML_ASSERT(ncols % QK_K == 0);
const int block_num_y = ceil_div(nrows, GGML_SYCL_MMV_Y);
constexpr size_t num_subgroups = 16;
GGML_ASSERT(block_num_y % num_subgroups == 0);
// Round up to a whole number of subgroup-sized workgroups; out-of-range rows are skipped inside the kernel.
constexpr size_t num_subgroups = WARP_SIZE;
const int block_num_y = ceil_div(nrows, GGML_SYCL_MMV_Y * (int) num_subgroups) * (int) num_subgroups;
const sycl::range<3> global_size(1, GGML_SYCL_MMV_Y, block_num_y * WARP_SIZE);
const sycl::range<3> workgroup_size(1, GGML_SYCL_MMV_Y, num_subgroups * WARP_SIZE);