Measured at a live KV length of 34816 (32768 depth plus one 2048 ubatch),
on Qwen3.8 27B Q4_K_S:
per tensor 4 * 34816 * 256 * 2 B = 71.3 MB
staged per call K and V, so 2x = 142.6 MB
traffic per call read once, write once = 285.2 MB
traffic per ubatch 285.2 MB * 16 calls = 4.56 GB
One ubatch is one ggml_cgraph submission (llama_context::process_ubatch ->
graph_compute), so that 4.56 GB is the cost of a single 2048-token prefill
chunk, and it scales with the live KV length: the first ubatch of the same run,
at seq = 2048, moves 0.27 GB.
Reproduce the two measured inputs with:
GGML_SCHED_DEBUG=2 llama-bench -m MODEL -p 8 -n 0 -r 1 -ngl 0 \
-fa on -ctk f16 -ctv f16 -v > nd.txt 2>&1
grep -E 'n_layer|n_head_kv|n_embd_head_k' nd.txt
awk '/node # 0 /{g++} g==1 && /\(FLASH_ATTN\)/{n++} END{print n+0}' nd.txt
Kernel is a port of `ggml-cuda/fwht.cu`
(us/run, median):
```
m x n x k GEMM FWHT speedup
64 x 1 x 64 10.20 2.93 3.48x
64 x 2048 x 64 10.75 2.71 3.97x
128 x 1 x 128 10.33 2.88 3.59x
128 x 32 x 128 9.20 2.77 3.33x
128 x 2048 x 128 16.46 2.76 5.95x
256 x 1 x 256 10.19 2.77 3.68x
256 x 2048 x 256 16.69 3.41 4.89x
512 x 2048 x 512 54.16 12.89 4.20x
```
Adjusts the thread/block count to be proportional to the size
of the quant, reducing under/over subscription.
Largest perf improvement is the q4_0 -> f32 path, with, on
a Arc 70, throughput goes from 20.21 GB/s to 158.19 GB/s
The rest of the quants are flat in performance uplift.
* tests: add SWIGLU perf cases
perf mode had no GLU coverage. Adds SWIGLU at 17408 columns, 512 and
2048 tokens, f16 and f32, with the operands both fused and split.
* sycl: consolidate fused-GLU kernels
They differed only in which op_* they called, so take the op as an argument and share a common launcher.
Their block sizes were all 256, so launch geometry is unchanged;
SYCL_GELU_BLOCK_SIZE and SYCL_SILU_BLOCK_SIZE lose their last users so are dropped.
* sycl: contiguous fast path for the fused GLU ops
o0 == n and o1 == n collapse the de-interleave index math to the
identity, so dispatch a flat kernel in that case. It fires for
ggml_glu_split with packed operands; a fused [gate|up] tensor keeps the
strided path. test-backend-ops perf -o SWIGLU on an Arc Pro B70: split
+14% f16 and +4% f32, fused unchanged.
* sycl: parallelize the non-contiguous concat kernel
Launch geometry only: the non-contiguous concat kernel launched a single-lane
work-group (1, 1, 1), now it will launch a (1, 1, SYCL_CONCAT_BLOCK_SIZE) one.
SYCL_CONCAT_BLOCK_SIZE is defined in `ggml/src/ggml-sycl/presets.hpp`.
llama-bench (Arc Pro B70, Qwen3.6-27B-UD-Q4_K_XL, -fa on, q8_0 KV),
on top of upstream master: pp2048 920 -> 1006 t/s (+9.4%)
* sycl: cap non-contiguous concat block at ne0
* sycl: make non-contiguous concat block width env-tunable (GGML_SYCL_CONCAT_BLOCK_SIZE)
* Revert "sycl: make non-contiguous concat block width env-tunable (GGML_SYCL_CONCAT_BLOCK_SIZE)"
This reverts commit 2709909e79.
