* [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.
* [SYCL] Fix Q8_0 reorder: add missing dequantize path for GEMM
The Q8_0 reorder optimization (#21527) was missing a reorder-aware
dequantizer for the GEMM code path used during prompt processing.
After token generation reordered Q8_0 weights (via DMMV/MMVQ), the
next prompt processing pass would read them with the standard
dequantizer, producing garbage output.
Add dequantize_block_q8_0_reorder() and wire it into both
ggml_get_to_fp16_sycl() and ggml_get_to_fp32_sycl(), matching the
pattern already used by Q4_0, Q4_K, and Q6_K.
Fixes#21589
AI (Claude) was used to assist with root cause investigation and
writing the kernel code. All code was human-reviewed and tested
on real hardware.
* SYCL: fix reorder crash when device memory is full
The reorder optimization allocates a temporary buffer the full size of
the weight tensor on the device. When VRAM is nearly full (large models
on a single GPU), this allocation fails and the subsequent memcpy crashes
on a NULL pointer.
Fix: try device allocation first, fall back to host memory if device
memory is full. The reorder kernel still works correctly reading from
host memory over PCIe. This is slower for the one-time reorder (~21 t/s
vs ~38 t/s on Intel Arc Pro B70), but the optimization is preserved for
all subsequent inference. If both device and host allocation fail, skip
the reorder and fall back to the unoptimized kernel path.
Also fixes a bug where opt_for_reorder() marked tensors as reordered
even when the reorder was skipped due to allocation failure. This caused
DMMV/MMVQ kernels to read the original AoS data as if it were SoA,
producing garbage output or NaN results.
Tested on Intel Arc Pro B70 (32GB) with Q8_0, Q4_K_M models. Coding was
AI-assisted (Claude), reviewed and tested on hardware by a human.
Fixes#20478
* SYCL: add RAII temp buffer class + macro guard for host fallback
Replace sycl_ext_malloc_with_fallback/sycl_ext_free_fallback free
functions with sycl_reorder_temp_buffer RAII class. The host_fallback
bool is now a private member, and cleanup happens automatically at
scope exit.
Add GGML_SYCL_HOST_MEM_FALLBACK cmake option (default ON) to guard
the host memory fallback code path. Device access to host memory
requires Linux kernel 6.8+ (Ubuntu 26.04+); users on older kernels
can set -DGGML_SYCL_HOST_MEM_FALLBACK=OFF to disable it.
Addresses arthw's review on PR #21638.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
* SYCL: document GGML_SYCL_HOST_MEM_FALLBACK build option in SYCL.md
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
* SYCL: add reorder-aware DMMV dequantizers for Q4_K and Q6_K
Q4_K and Q6_K had reorder support for MMVQ and GEMM paths but not
DMMV. When the DMMV path encountered reordered data it would abort.
Add DMMV kernels that read from the SOA reorder layout for both
types. Same math as the non-reorder versions, different memory
access pattern.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---------
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Extend the existing reorder optimization to Q8_0. The reorder
separates scale factors from weight data for coalesced memory
access -- was implemented for Q4_0/Q4_K/Q6_K but Q8_0 was missing.
On Arc Pro B70 (Xe2), Q8_0 tg goes from 4.88 to 15.24 t/s (3.1x)
on Qwen3.5-27B. BW utilization: 21% -> 66%.
The key fix beyond the kernels: Q8_0 was missing from the type
check in ggml_backend_sycl_buffer_init_tensor() that allocates
the extra struct carrying the reorder flag -- so the optimization
was silently skipped.
AI (Claude) was used to assist with root cause investigation and
writing the kernel code. All code was human-reviewed and tested
on real hardware.
Fixes: #21517
