Avx512

AVX-512 全系统优化技能

概述

AVX-512 是 Intel 的高级向量扩展指令集，支持 512 位向量运算，可显著提升计算密集型任务的性能。

性能提升

核心优化模块

1. 向量运算优化

#include <immintrin.h>

// AVX-512 点积 (1024 维向量)
inline float dot_product_avx512(const float* a, const float* b, size_t dim) {
    __m512 sum = _mm512_setzero_ps();
    
    for (size_t i = 0; i < dim; i += 16) {
        __m512 va = _mm512_loadu_ps(a + i);
        __m512 vb = _mm512_loadu_ps(b + i);
        sum = _mm512_fmadd_ps(va, vb, sum);  // FMA: va * vb + sum
    }
    
    return _mm512_reduce_add_ps(sum);
}

// 批量余弦相似度
void batch_cosine_avx512(
    const float* query,
    const float* const* vectors,
    size_t num_vectors,
    size_t dim,
    float* scores
) {
    float query_norm = 0.0f;
    __m512 qn = _mm512_setzero_ps();
    for (size_t i = 0; i < dim; i += 16) {
        __m512 q = _mm512_loadu_ps(query + i);
        qn = _mm512_fmadd_ps(q, q, qn);
    }
    query_norm = sqrtf(_mm512_reduce_add_ps(qn));
    
    #pragma omp parallel for
    for (size_t i = 0; i < num_vectors; ++i) {
        float dot = dot_product_avx512(query, vectors[i], dim);
        float norm = vector_norm_avx512(vectors[i], dim);
        scores[i] = dot / (query_norm * norm + 1e-8f);
    }
}

2. 加密运算优化

// AVX-512 AES-GCM 加速
void aes_gcm_encrypt_avx512(
    const __m512i* plaintext,
    __m512i* ciphertext,
    size_t blocks,
    const __m512i* key,
    __m512i* counter
) {
    for (size_t i = 0; i < blocks; ++i) {
        // AES-NI + AVX-512 组合
        __m512i ctr = _mm512_add_epi64(*counter, _mm512_set1_epi64(i));
        __m512i encrypted = aes_encrypt_avx512(ctr, key);
        ciphertext[i] = _mm512_xor_si512(plaintext[i], encrypted);
    }
}

// SHA-256 加速
void sha256_avx512(const uint8_t* data, size_t len, uint8_t* hash) {
    // 使用 AVX-512 并行处理 4 个 SHA-256 块
    __m512i state = _mm512_setzero_si512();
    
    for (size_t i = 0; i < len; i += 256) {
        __m512i block = _mm512_loadu_si512((__m512i*)(data + i));
        state = sha256_round_avx512(state, block);
    }
    
    _mm512_storeu_si512((__m512i*)hash, state);
}

3. 内存操作优化

// AVX-512 内存复制
void memcpy_avx512(void* dst, const void* src, size_t size) {
    __m512i* d = (__m512i*)dst;
    const __m512i* s = (const __m512i*)src;
    
    size_t i = 0;
    for (; i + 16 <= size; i += 64) {
        __m512i data = _mm512_loadu_si512(s + i/64);
        _mm512_storeu_si512(d + i/64, data);
    }
    
    // 处理剩余字节
    if (i < size) {
        __mmask64 mask = (1ULL << (size - i)) - 1;
        __m512i data = _mm512_maskz_loadu_epi8(mask, (const void*)(s + i/64));
        _mm512_mask_storeu_epi8(d + i/64, mask, data);
    }
}

// 内存比较
int memcmp_avx512(const void* a, const void* b, size_t size) {
    const __m512i* pa = (const __m512i*)a;
    const __m512i* pb = (const __m512i*)b;
    
    for (size_t i = 0; i < size; i += 64) {
        __m512i va = _mm512_loadu_si512(pa + i/64);
        __m512i vb = _mm512_loadu_si512(pb + i/64);
        
        __mmask64 diff = _mm512_cmpneq_epi8_mask(va, vb);
        if (diff) {
            return _mm_popcnt_u64(diff & ((1ULL << (size - i)) - 1));
        }
    }
    return 0;
}

4. 字符串处理优化

// AVX-512 字符串查找
const char* strstr_avx512(const char* haystack, const char* needle) {
    size_t needle_len = strlen(needle);
    __m512i needle_vec = _mm512_loadu_si512((__m512i*)needle);
    
    for (const char* p = haystack; *p; p += 64) {
        __m512i hay = _mm512_loadu_si512((__m512i*)p);
        __mmask64 match = _mm512_cmpeq_epi8_mask(hay, needle_vec);
        
        if (match) {
            // 检查完整匹配
            while (match) {
                int idx = __builtin_ctzll(match);
                if (memcmp_avx512(p + idx, needle, needle_len) == 0) {
                    return p + idx;
                }
                match &= match - 1;
            }
        }
    }
    return nullptr;
}

六层架构集成

编译选项

# GCC/Clang
g++ -O3 -mavx512f -mavx512dq -mavx512bw -mavx512vl \
    -ffast-math -funroll-loops \
    -o optimized output.cpp

# 检测 AVX-512 支持
lscpu | grep -i avx512

运行时检测

bool has_avx512() {
    uint32_t eax, ebx, ecx, edx;
    __cpuid_count(7, 0, eax, ebx, ecx, edx);
    return (ebx & (1 << 16)) != 0;  // AVX512F
}

// 自动选择最优实现
void (*vector_search)(const float*, const float* const*, size_t, size_t, float*);

if (has_avx512()) {
    vector_search = batch_cosine_avx512;
} else if (has_avx2()) {
    vector_search = batch_cosine_avx2;
} else {
    vector_search = batch_cosine_scalar;
}

版本

• V1.0.0
• 创建日期: 2026-04-10