Max Krasnyansky
192067b72d
* hexagon: use non-host bufs by default and make the backend fully async * hex-hb: remove optional hostbuf support and fix async copy * hex-unary: relax supported unary check * hex-bufs: use same get_alignment for host bufs * snapdragon: bump android_platform to 34 * hex-rows: super hacky get/set rows for q8_0 * hex-get-rows: fix q8_0 * hex-get-rows: supprot for f16 and cleanup for q8_0 * hex-get-rows: generic macros and specialized thread funcs * hex-get-rows: add DMA pipeline, vtcm_layout and kernel params * hex-set-rows: fix q8_0 support, add dma and tracing * hex-tests: override nmse threshold for HTP of Q8_0 quants * hex-fa: add support for Q8_0 with inplace dequantizers * hex-get-rows: simplify type dispatch * hex-rows: simplify GET/SET_ROWS DMA pipeline * hex-async: add events, set/get-tensor-async and rest of the async api support * hex-repack: use slice instead of expert in repack functions * hex-cpy: update event/async-cpy logging * hex-set-rows: optimize smaller tensors * hex-geglu: fix perf regression with larger tensors * hex-get-rows: add missing header * hex-set-rows: add missing header * hex-bufs: ressurect GGML_HEXAGON_HOSTBUF but disable it by default * hexagon: do not reject ops with non-heaxon buffers * hex-get-rows: apply >=32 restriction only for q8_0 * hex-res: bump vtcm acquire timeout to 10 seconds * hex-bufs: add support for cloning buffers between sessions to speed up tensor copies * hex-async: rework event recording and batch flushing and integrate with meta backend * hex-bufs: improved handling of repacked tensors * hex-repack: handle get_tensor_2d offsets * hex-dev: add support for devices with multiple NPUs * hex-sync: add support for sync tokens to synchronize npu devices for async splits * hex-mmap: cleanup mmap calls and add a retry for robustness * hex-sync: add failsafe if sync wait gets stuck * hex-sync: use sync_seq to check for completed events * hex-sync: rotate tokens for extra robustness * hex-devs: add supprot for legacy device names for now * hex-bufs: add support for auto-cloning buffers from diff sessions * hex-fusion: simplify and optimize htp-opnode fusion handling * hex-sync: override opnode name so that it shows up in the profiles * hex-trace: update scripts to handle multiple devices * hex-sync: bump the size of the opbatch queue and number of sync tokens * hex-cpy-sync: do not explicitly flush opbatches in cpy_tensor_async and add support for cpy-dma * hex-sync: add graph-flush threshold to avoid single op batches * hex-sync: add sync_peer so that we can flush peers we depend on during cross-device ops * hex-bufs: introduce tensor->extra and shadow_bufs for repacking * hex-l2: flush tiny tensors inline * hex-sync: use explicit l2flush for sync tokens * hex-extra: track weight flags via tensor extra * hex-fence: rename sync to fence * hex-repack: proper handling of set-tensor-2d in the shadow_buf * hex-trace: remove obsolete opstage mask that we used for profiling * hex-env: remove obsolete use_hmx variable * hexagon: new unified run.py and build.py and updated docs * snapdragon: update run script to auto-escapt test-backend-op -p argument * hex-scripts: fix trailing spaces * hex-scripts: fix flake8 warnings * snapdragon: cleanup dst lib/bin dirs before copying new build * hex-ops: add support for allreduce * hex-ar: improved allreduce with dma pipeline * hex-ar: align macros * hex-ar: consistent use of fence_seq * hex-ar: add AR_SELECT env var to select ALLREDUCE kernel or fallback * hex-ar: add proper synchronize handling for ALLREDUCE * hex-opbatch: looks like we now just rely on backend.synchronise to flush the batches, no need to flush them by threshold * hex-ar: bump block size to improve dma efficiency * hex-ar: fused ALLREDUCE+ADD * hex-ar: cleaner fence buffer management * hex-ar: futher allreduce tweaking to remove race conditions * hex-ar: add simple solver and remove non-dma kernels * hex-ar: add row-broadcast to fuse with bias ADD * hex-fence: pass seq numbers via op_params * hex-ar: allow for both entry/exit seq for completing entry wait * hex-ar: align macros * hex-ar: do not refetch broadcast row * hex-fusion: move all fusion into opbatch::add_op for consistency with ALLREDUCE and things * hex-fusion: fix incorrect MUL_MAT reordering * hex-mm: make fused 2x and 3x matmuls more generic * hex-fusion: move tensor fusion tagging to graph_compute * hexagon: make sure to copy tensor->extra by value * hex-get-rows: fix offset calc with row-chunking * hex-repack: get_tensor_2d fixes for non-zero offsets * snapdragon: make profile/trace scripts more robust and donot mix stdout/stderr by default * hex-devices: use legacy device nameing by default to ease the transition * hex-devices: hardcode CDSP domain IDs for current devices for now * hex-optrace: improve multi-NPU timestamp alignment and overall handling of cycle values * hex-optrace: more robust handling of the fence events
5.8 KiB
Hexagon backend developer details
Backend libraries
The Hexagon backend consist of two parts:
-
libggml-hexagonThis is the regular CPU-side GGML backend library, either shared or statically linked -
libggml-htp-vNNThis is the NPU-side (HTP stands for Hexagon Tensor Processor) shared library that contains the Op dispatcher and kernels. The correct library is selected automatically at runtime based on the HW version.
Here is an example of the build artifacts
~/src/llama.cpp$ ls -l pkg-adb/llama.cpp/lib/libggml*
pkg-adb/llama.cpp/lib/libggml-base.so
pkg-adb/llama.cpp/lib/libggml-cpu.so
pkg-adb/llama.cpp/lib/libggml-hexagon.so <<< CPU library
pkg-adb/llama.cpp/lib/libggml-htp-v73.so <<< HTP op/kernels for Hexagon v73
pkg-adb/llama.cpp/lib/libggml-htp-v75.so
pkg-adb/llama.cpp/lib/libggml-htp-v79.so
pkg-adb/llama.cpp/lib/libggml-htp-v81.so
Memory buffers
Hexagon NPU backend takes advantage of the Snapdragon's unified memory model where all buffers are fully accessible by the CPU and GPU. The NPU does have a dedicated tightly-coupled memory called VTCM but that memory is used only for intermediate data (e.g. dynamically quantized tensors) or temporary data (chunks of the weight tensors fetched via DMA).
Please note that currently the Hexagon backend does not implement SET/GET_ROWS Ops because there is no advantage in offloading those to the NPU at this point.
The backend does allocates non-host buffers for the tensors with datatypes that require repacking: Q4_0, Q8_0, MXFP4. From the MMU perspective these buffers are still regular buffers (normal access by the CPU) they are marked as non-host simply to force the repacking.
Large model handling
Hexagon NPU sessions (aka Process Domains (PD) in the Hexagon SDK) are limited to a maximum memory mapping window of around 3.5GB.
In llama.cpp/GGML, each Hexagon session is mapped to a single GGML backend device (e.g., HTP0:0, HTP0:1, etc. when using
GGML_HEXAGON_DEVICES, or HTP0, HTP1 in legacy mode).
To support running models larger than 3.5GB on a single device, the Hexagon backend dynamically maps and unmaps execution buffers during the graph execution cycle to stay within the Process Domain window. This enables large models to run successfully on a single NPU device.
Alternatively, users can choose to use standard llama.cpp/GGML layer-splitting mode to partition and split the model across multiple Hexagon devices or virtual sessions (which behave like multiple GPUs from the offload and splitting perspective).
Here is an example of running GPT-OSS-20B model on a Snapdragon device using 4 virtual sessions on a single NPU (physical index 0).
~/src/llama.cpp$ ./scripts/snapdragon/run.py --target adb --devices HTP0:0,HTP0:1,HTP0:2,HTP0:3 -- llama-cli --load-mode none -m /data/local/tmp/gguf/gpt-oss-20b-Q4_0.gguf -t 4 --ctx-size 8192 --batch-size 128 -ctk q8_0 -ctv q8_0 -fa on -ngl 99 -no-cnv -f surfing.txt
...
llama_model_loader: - type f32: 289 tensors
llama_model_loader: - type q4_0: 96 tensors
llama_model_loader: - type q8_0: 2 tensors
llama_model_loader: - type mxfp4: 72 tensors
...
load_tensors: offloaded 25/25 layers to GPU
load_tensors: CPU model buffer size = 1182.09 MiB
load_tensors: HTP0:1 model buffer size = 2512.58 MiB
load_tensors: HTP0:3 model buffer size = 2093.83 MiB
load_tensors: HTP0:0 model buffer size = 2931.34 MiB
load_tensors: HTP0:2 model buffer size = 2512.58 MiB
...
llama_context: n_ctx_per_seq (8192) < n_ctx_train (131072) -- the full capacity of the model will not be utilized
llama_context: CPU output buffer size = 0.77 MiB
llama_kv_cache_iswa: creating non-SWA KV cache, size = 8192 cells
llama_kv_cache: HTP0:1 KV buffer size = 25.50 MiB
llama_kv_cache: HTP0:3 KV buffer size = 25.50 MiB
llama_kv_cache: HTP0:0 KV buffer size = 25.50 MiB
llama_kv_cache: HTP0:2 KV buffer size = 25.50 MiB
llama_kv_cache: size = 102.00 MiB ( 8192 cells, 12 layers, 1/1 seqs), K (q8_0): 51.00 MiB, V (q8_0): 51.00 MiB
llama_kv_cache_iswa: creating SWA KV cache, size = 256 cells
llama_kv_cache: HTP0:1 KV buffer size = 0.80 MiB
llama_kv_cache: HTP0:3 KV buffer size = 0.53 MiB
llama_kv_cache: HTP0:0 KV buffer size = 1.06 MiB
llama_kv_cache: HTP0:2 KV buffer size = 0.80 MiB
llama_kv_cache: size = 3.19 MiB ( 256 cells, 12 layers, 1/1 seqs), K (q8_0): 1.59 MiB, V (q8_0): 1.59 MiB
llama_context: HTP0:0 compute buffer size = 16.06 MiB
llama_context: HTP0:1 compute buffer size = 16.06 MiB
llama_context: HTP0:2 compute buffer size = 16.06 MiB
llama_context: HTP0:3 compute buffer size = 16.06 MiB
llama_context: CPU compute buffer size = 98.19 MiB
...
llama_perf_context_print: prompt eval time = 3843.67 ms / 197 tokens ( 19.51 ms per token, 51.25 tokens per second)
llama_perf_context_print: eval time = 1686.13 ms / 31 runs ( 54.39 ms per token, 18.39 tokens per second)
llama_perf_context_print: total time = 6266.30 ms / 228 tokens
llama_perf_context_print: graphs reused = 30
llama_memory_breakdown_print: | memory breakdown [MiB] | total free self model context compute unaccounted |
llama_memory_breakdown_print: | - HTP0:0 (Hexagon) | 2048 = 2048 + ( 0 = 0 + 0 + 0) + 0 |
llama_memory_breakdown_print: | - HTP0:1 (Hexagon) | 2048 = 2048 + ( 0 = 0 + 0 + 0) + 0 |
llama_memory_breakdown_print: | - HTP0:2 (Hexagon) | 2048 = 2048 + ( 0 = 0 + 0 + 0) + 0 |
llama_memory_breakdown_print: | - HTP0:3 (Hexagon) | 2048 = 2048 + ( 0 = 0 + 0 + 0) + 0 |
llama_memory_breakdown_print: | - Host | 1476 = 1208 + 105 + 162 |