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llama.cpp/ggml/src/ggml-sycl/gemm.hpp
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Akarshan Biswas 225088ea76 sycl: Improve mul_mat_id memory efficiency and add BF16 fast path (#22119)
* sycl: size mul_mat_id staging buffers by routed rows

Previously src1_contiguous/dst_contiguous in ggml_sycl_mul_mat_id were
sized to ggml_nelements(src1/dst), which over-allocates when ne12 > 1
and can fail with UR_RESULT_ERROR_OUT_OF_HOST_MEMORY on Level Zero for
MoE models (notably with --cpu-moe). Size them by the actual number of
routed rows (ids->ne[1] * n_ids) instead.

* sycl: add bf16 mul_mat fast path via DNNL

When src0 is BF16 (commonly the case for lm_head / output.weight), the
existing f16 path is skipped because bf16 isn't covered, and the f32
fallback dequantizes the entire src0 slab to f32 in a single pool alloc
(row_diff*ne00 floats). For large-vocab models this can reach several
GB and fail with UR_RESULT_ERROR_OUT_OF_HOST_MEMORY on Level Zero.

Add a bf16xbf16 -> f32 DNNL matmul fast path that uses the bf16 storage
in place and only materializes a small src1 bf16 conversion buffer. bf16
matmul accumulates in f32, so it's correct even when the op requests
GGML_PREC_F32 (as lm_head does).

- gemm.hpp: map bfloat16 to dnnl::memory::data_type::bf16.
- convert.{hpp,cpp}: expose ggml_get_to_bf16_sycl for f32/f16/bf16 -> bf16.
- ggml-sycl.cpp: take the bf16 path early in ggml_sycl_op_mul_mat_sycl
  when DNNL and GGML_SYCL_HAS_BF16 are both available.
2026-04-22 20:32:56 +08:00

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3.2 KiB
C++

//
// MIT license
// Copyright (C) 2024 Intel Corporation
// SPDX-License-Identifier: MIT
//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
#ifndef GGML_SYCL_GEMM_HPP
#define GGML_SYCL_GEMM_HPP
#include "ggml-sycl.h"
#if GGML_SYCL_DNNL
#include "dnnl.hpp"
#include "dnnl_sycl.hpp"
class DnnlGemmWrapper {
public:
using dt = dnnl::memory::data_type;
using tag = dnnl::memory::format_tag;
template<typename T>
static constexpr dt to_dt() {
if constexpr (std::is_same_v<T, float>) return dt::f32;
else if constexpr (std::is_same_v<T, sycl::half>) return dt::f16;
#ifdef GGML_SYCL_HAS_BF16
else if constexpr (std::is_same_v<T, sycl::ext::oneapi::bfloat16>) return dt::bf16;
#endif
else static_assert(0);
}
static void gemm(ggml_backend_sycl_context & ctx, int m, int n, int k,
const void * a, dt at, dnnl_dim_t stra0, dnnl_dim_t stra1, dnnl_dim_t stra2,
const void * b, dt bt, dnnl_dim_t strb0, dnnl_dim_t strb1, dnnl_dim_t strb2,
void * c, dt ct, const queue_ptr & q, dnnl_dim_t batches_a, dnnl_dim_t batches_b) {
auto stream = ctx.stream_dnnl(q);
auto eng = ctx.engine_dnnl(q);
dnnl::memory::dims a_dims = {batches_a, m, k };
dnnl::memory::dims a_strides = {stra2, stra1, stra0};
const auto a_in_md = dnnl::memory::desc(a_dims, at, a_strides);
dnnl::memory::dims b_dims = {batches_b, k, n };
dnnl::memory::dims b_strides = {strb2, strb0, strb1};
const auto b_in_md = dnnl::memory::desc(b_dims, bt, b_strides);
dnnl::memory::dims c_dims = { std::max(batches_a, batches_b), m, n};
dnnl::memory::dims c_strides = {m*n, 1, m };
const auto c_md = dnnl::memory::desc(c_dims, ct, c_strides);
dnnl::primitive_attr primitive_attr;
primitive_attr.set_scratchpad_mode(dnnl::scratchpad_mode::user);
#ifdef GGML_SYCL_F16
primitive_attr.set_fpmath_mode(dnnl::fpmath_mode::f16);
#endif
auto a_mem = dnnl::memory(a_in_md, eng, const_cast<void*>(a));
auto b_mem = dnnl::memory(b_in_md, eng, const_cast<void*>(b));
auto matmul_pd = dnnl::matmul::primitive_desc(eng, a_in_md, b_in_md, c_md, primitive_attr);
auto c_mem = dnnl::memory(matmul_pd.dst_desc(), eng, c);
auto scratchpad_md = matmul_pd.scratchpad_desc();
auto scratchpad_mem = ctx.get_scratchpad_mem(scratchpad_md, eng, q);
auto matmul_prim = dnnl::matmul(matmul_pd);
std::unordered_map<int, dnnl::memory> matmul_args;
matmul_args.insert({ DNNL_ARG_SRC, a_mem });
matmul_args.insert({ DNNL_ARG_WEIGHTS, b_mem });
matmul_args.insert({ DNNL_ARG_DST, c_mem });
matmul_args.insert({ DNNL_ARG_SCRATCHPAD, scratchpad_mem });
matmul_prim.execute(stream, matmul_args);
}
static void row_gemm(ggml_backend_sycl_context & ctx, int m, int n, int k,
const void * a, dt at, const void * b, dt bt, void * c, dt ct, const queue_ptr & q) {
gemm(ctx, m, n, k, a, at, 1, k, k * m, b, bt, 1, k, n * k, c, ct, q, 1, 1);
}
};
#endif
#endif // GGML_SYCL_GEMM_HPP