我正在英特尔®至强®上实现超快速弹出，因为它是各种生物信息学软件的性能热点。
我已经实现了五段代码，
#if defined(__MIC__)
#include <zmmintrin.h>
__attribute__((align(64))) static const uint32_t POPCOUNT_4bit[16] = {0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};
__attribute__((align(64))) static const uint32_t MASK_4bit[16] = {0xF, 0xF, 0xF, 0xF, 0xF, 0xF, 0xF, 0xF, 0xF, 0xF, 0xF, 0xF, 0xF, 0xF, 0xF, 0xF};
inline uint64_t vpu_popcount1(uint64_t* buf, size_t n) {
register size_t result = 0;
size_t i;
register const __m512i popcnt = _mm512_load_epi32((void*)POPCOUNT_4bit);
register const __m512i mask = _mm512_load_epi32((void*)MASK_4bit);
register __m512i total;
register __m512i shuf;
#pragma unroll(8)
for (i = 0; i < n; i+=8) {
shuf = _mm512_load_epi32(&buf[i]);
_mm_prefetch((const char *)&buf[i+256], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+64], _MM_HINT_T0); // vprefetch0
total = _mm512_setzero_epi32();
total = _mm512_add_epi32(_mm512_permutevar_epi32(_mm512_and_epi32(shuf, mask), popcnt), total);
total = _mm512_add_epi32(_mm512_permutevar_epi32(_mm512_and_epi32(_mm512_srli_epi32(shuf, 4), mask), popcnt), total);
total = _mm512_add_epi32(_mm512_permutevar_epi32(_mm512_and_epi32(_mm512_srli_epi32(shuf, 8), mask), popcnt), total);
total = _mm512_add_epi32(_mm512_permutevar_epi32(_mm512_and_epi32(_mm512_srli_epi32(shuf, 12), mask), popcnt), total);
total = _mm512_add_epi32(_mm512_permutevar_epi32(_mm512_and_epi32(_mm512_srli_epi32(shuf, 16), mask), popcnt), total);
total = _mm512_add_epi32(_mm512_permutevar_epi32(_mm512_and_epi32(_mm512_srli_epi32(shuf, 20), mask), popcnt), total);
total = _mm512_add_epi32(_mm512_permutevar_epi32(_mm512_and_epi32(_mm512_srli_epi32(shuf, 24), mask), popcnt), total);
total = _mm512_add_epi32(_mm512_permutevar_epi32(_mm512_and_epi32(_mm512_srli_epi32(shuf, 28), mask), popcnt), total);
/* Reduce add, which is analogous to SSSE3's PSADBW instruction,
is not implementated as a single instruction in VPUv1, thus
emulated by multiple instructions*/
result += _mm512_reduce_add_epi32(total);
}
return result;
}
__attribute__((align(64))) static const unsigned magic[] = {\
0x55555555, 0x55555555, 0x55555555, 0x55555555,\
0x55555555, 0x55555555, 0x55555555, 0x55555555,\
0x55555555, 0x55555555, 0x55555555, 0x55555555,\
0x55555555, 0x55555555, 0x55555555, 0x55555555,\
0x33333333, 0x33333333, 0x33333333, 0x33333333,\
0x33333333, 0x33333333, 0x33333333, 0x33333333,\
0x33333333, 0x33333333, 0x33333333, 0x33333333,\
0x33333333, 0x33333333, 0x33333333, 0x33333333,\
0x0F0F0F0F, 0x0F0F0F0F, 0x0F0F0F0F, 0x0F0F0F0F,\
0x0F0F0F0F, 0x0F0F0F0F, 0x0F0F0F0F, 0x0F0F0F0F,\
0x0F0F0F0F, 0x0F0F0F0F, 0x0F0F0F0F, 0x0F0F0F0F,\
0x0F0F0F0F, 0x0F0F0F0F, 0x0F0F0F0F, 0x0F0F0F0F,\
0x00FF00FF, 0x00FF00FF, 0x00FF00FF, 0x00FF00FF,\
0x00FF00FF, 0x00FF00FF, 0x00FF00FF, 0x00FF00FF,\
0x00FF00FF, 0x00FF00FF, 0x00FF00FF, 0x00FF00FF,\
0x00FF00FF, 0x00FF00FF, 0x00FF00FF, 0x00FF00FF,\
0x0000FFFF, 0x0000FFFF, 0x0000FFFF, 0x0000FFFF,\
0x0000FFFF, 0x0000FFFF, 0x0000FFFF, 0x0000FFFF,\
0x0000FFFF, 0x0000FFFF, 0x0000FFFF, 0x0000FFFF,\
0x0000FFFF, 0x0000FFFF, 0x0000FFFF, 0x0000FFFF,\
0x000000FF, 0x000000FF, 0x000000FF, 0x000000FF,\
0x000000FF, 0x000000FF, 0x000000FF, 0x000000FF,\
0x000000FF, 0x000000FF, 0x000000FF, 0x000000FF,\
0x000000FF, 0x000000FF, 0x000000FF, 0x000000FF
};
inline uint64_t vpu_popcount2(uint64_t* buf, size_t n) {
register size_t result = 0;
size_t i;
register const __m512i B0 = _mm512_load_epi32((void*)(magic+0));
register const __m512i B1 = _mm512_load_epi32((void*)(magic+16));
register const __m512i B2 = _mm512_load_epi32((void*)(magic+32));
register const __m512i B3 = _mm512_load_epi32((void*)(magic+48));
register const __m512i B4 = _mm512_load_epi32((void*)(magic+64));
register __m512i total;
register __m512i shuf;
#pragma unroll(8)
for (i = 0; i < n; i+=8) {
shuf = _mm512_load_epi32(&buf[i]);
_mm_prefetch((const char *)&buf[i+512], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+64], _MM_HINT_T0); // vprefetch0
total = _mm512_sub_epi32(shuf, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf,1)));
total = _mm512_add_epi32(_mm512_and_epi32(B1, total), _mm512_and_epi32(B1,_mm512_srli_epi32(total,2)));
total = _mm512_and_epi32(B2, _mm512_add_epi32(total, _mm512_srli_epi32(total,4)));
total = _mm512_and_epi32(B3, _mm512_add_epi32(total, _mm512_srli_epi32(total,8)));
total = _mm512_and_epi32(B4, _mm512_add_epi32(total, _mm512_srli_epi32(total,16)));
/* Reduce add, which is analogous to SSSE3's PSADBW instruction,
is not implementated as a single instruction in VPUv1, thus
emulated by multiple instructions*/
result += _mm512_reduce_add_epi32(total);
}
return result;
}
inline uint64_t vpu_popcount3(uint64_t* buf, size_t n) {
register size_t result = 0;
size_t i;
register const __m512i B0 = _mm512_load_epi32((void*)(magic+0));
register const __m512i B1 = _mm512_load_epi32((void*)(magic+16));
register const __m512i B2 = _mm512_load_epi32((void*)(magic+32));
register const __m512i B3 = _mm512_load_epi32((void*)(magic+48));
register const __m512i B4 = _mm512_load_epi32((void*)(magic+64));
register __m512i total;
register __m512i shuf;
#pragma unroll(4)
for (i = 0; i < n; i+=16) {
shuf = _mm512_load_epi32(&buf[i]);
result += _mm_countbits_64(buf[i+8]);
_mm_prefetch((const char *)&buf[i+512], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+576], _MM_HINT_T1); // vprefetch1
result += _mm_countbits_64(buf[i+9]);
_mm_prefetch((const char *)&buf[i+64], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[i+128], _MM_HINT_T0); // vprefetch0
total = _mm512_sub_epi32(shuf, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf,1)));
result += _mm_countbits_64(buf[i+10]);
total = _mm512_add_epi32(_mm512_and_epi32(B1, total), _mm512_and_epi32(B1,_mm512_srli_epi32(total,2)));
result += _mm_countbits_64(buf[i+11]);
total = _mm512_and_epi32(B2, _mm512_add_epi32(total, _mm512_srli_epi32(total,4)));
result += _mm_countbits_64(buf[i+12]);
total = _mm512_and_epi32(B3, _mm512_add_epi32(total, _mm512_srli_epi32(total,8)));
result += _mm_countbits_64(buf[i+13]);
total = _mm512_and_epi32(B4, _mm512_add_epi32(total, _mm512_srli_epi32(total,16)));
result += _mm_countbits_64(buf[i+14]);
/* Reduce add, which is analogous to SSSE3's PSADBW instruction,
is not implementated as a single instruction in VPUv1, thus
emulated by multiple instructions*/
result += _mm512_reduce_add_epi32(total);
result += _mm_countbits_64(buf[i+15]);
}
return result;
}
/* Using VPU or SSE's machine intrinsic, CPUs not supporting SIMD
* will use compiler's implementation, the speed of which depends */
static inline size_t scalar_popcountu(unsigned *buf, size_t n) {
register size_t cnt = 0;
size_t i;
#pragma vector always
#pragma unroll(8)
for (i = 0; i < n; i++) {
cnt += _mm_countbits_32(buf[i]);
_mm_prefetch((const char *)&buf[i+512], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+64], _MM_HINT_T0); // vprefetch0
}
return cnt;
}
static inline size_t scalar_popcountlu(uint64_t *buf, size_t n) {
register size_t cnt = 0;
size_t i;
#pragma vector always
#pragma unroll(8)
for (i = 0; i < n; i++) {
cnt += _mm_countbits_64(buf[i]);
_mm_prefetch((const char *)&buf[i+512], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+64], _MM_HINT_T0); // vprefetch0
}
return cnt;
}
#endif
可以从https://www.dropbox.com/sh/b3sfqps19wa2oi4/iFQ9wQ1NTg
下载包含OpenMP支持的代码使用命令：
使用英特尔C / C ++编译器XE 13编译代码icc -debug inline-debug-info -O3 -mmic -fno-alias -ansi-alias -opt-streaming-stores always -ipo popcnt-mmic.cpp -o popcnt-mmic -vec-report=2 -openmp
代码在协处理器（61个核心）上本地运行，“122个线程”，线程亲和力使用导出“平衡”：
export OMP_NUM_THREADS=122;export KMP_AFFINITY=balanced
我正在使用Xeon Phi SE10p，B1踩踏，CentOS6.4 测试28兆字节（由rand（）填充）并迭代10000次，性能如下：
Buffer allocated at: 0x7f456b000000
OpenMP scalar_popcountu 4310169 us; cnt = 28439328
OpenMP scalar_popcountlu 1421139 us; cnt = 28439328
OpenMP vpu_popcount 1489992 us; cnt = 28439328
OpenMP vpu_popcount2 1109530 us; cnt = 28439328
OpenMP vpu_popcount3 951122 us; cnt = 28439328
“scalar_popcountu”和“scalar_popcountlu”分别使用“_mm_countbits_32”和“_mm_countbits_64”内在函数，它们使用标量“popcnt”指令。设置“#pragma vector always”要求编译器将加载和求和向量化为16个无符号整数或8个无符号长整数，尽管popcount本身仍然是标量指令。
vpu_popcount1的实现类似于SSSE3 popcount实现http://wm.ite.pl/articles/sse-popcount.html。但是，1）Xeon Phi不支持整数上的压缩字节操作（最小值是双字，又称32位）和2）它不实现“绝对差值的压缩总和”指令（如SSSE3中的_mm_sad_epu8），因此减少添加是由四组“vpermf32x4”，“vpaddd”和“movslq”的组合执行的。因此，实现生成的指令比原始SSSE3版本多得多。
vpu_popcount2的实现类似于SSE2 popcount实现（可以参考“Hacker's Delight”）。该实现生成的指令少于vpu_popcount1，并且速度提高了约30％。然而，繁琐的“减少添加”仍然是无法避免的。
vpu_popcount3的实现非常具有Xeon Phi。通过向量和标量运算的混合，它比vpu_popcount2快15％（在向量操作中标量运算的散布在我的实现中是休闲的，可以根据编译器生成的汇编代码重新排列标量运算，但预期的改进就我而言是有限的）。该改进基于以下观察：1）Xeon Phi是有序调度，2）每个时钟周期可以发出两个标量指令或“1向量+ 1个标量”指令。我将展开从8减少到4以避免寄存器文件饱和。
在每个函数中预先从内存到L2 8循环的显式预取以及从L2到L1 1循环的预先显式预取将L1命中率从0.38增加到0.994。
展开会使性能提高约15％。这是违反直觉的，因为Xeon Phi是有序调度。但unroll使icc编译器能够尽可能多地进行编译时调度。
我们是否有更多技术来提升表现？
Brian Nickerson的两段更快的代码，
OpenMP vpu_popcount2 1110737 us; cnt = 28439328
OpenMP vpu_popcount3 951459 us; cnt = 28439328
OpenMP vpu_popcount3_r 815126 us; cnt = 28439328
OpenMP vpu_popcount5 746852 us; cnt = 28439328
vpu_popcount3_revised：
inline uint64_t vpu_popcount3_revised(uint64_t* buf, size_t n) {
_mm_prefetch((const char *)&buf[0], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[8], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[16], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[24], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[32], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[40], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[48], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[56], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[64], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[72], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[80], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[88], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[96], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[104], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[112], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[120], _MM_HINT_T1); // vprefetch1
register size_t result;
size_t i;
register const __m512i B0 = _mm512_load_epi32((void*)(magic+0));
register const __m512i B1 = _mm512_load_epi32((void*)(magic+16));
register const __m512i B2 = _mm512_load_epi32((void*)(magic+32));
register const __m512i B3 = _mm512_load_epi32((void*)(magic+48));
register const __m512i B4 = _mm512_load_epi32((void*)(magic+64));
register __m512i total0;
register __m512i total1;
register __m512i shuf0;
register __m512i shuf1;
register __m512i result0;
register __m512i result1;
result0 = _mm512_setzero_epi32();
result1 = _mm512_setzero_epi32();
for (i = 0; i < n; i+=16) {
shuf0 = _mm512_load_epi32(&buf[i ]);
shuf1 = _mm512_load_epi32(&buf[i+8]);
_mm_prefetch((const char *)&buf[i+128], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+136], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+16], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[i+24], _MM_HINT_T0); // vprefetch0
total0 = _mm512_sub_epi32(shuf0, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf0,1)));
total1 = _mm512_sub_epi32(shuf1, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf1,1)));
total0 = _mm512_add_epi32(_mm512_and_epi32(B1, total0), _mm512_and_epi32(B1,_mm512_srli_epi32(total0,2)));
total1 = _mm512_add_epi32(_mm512_and_epi32(B1, total1), _mm512_and_epi32(B1,_mm512_srli_epi32(total1,2)));
total0 = _mm512_and_epi32(B2, _mm512_add_epi32(total0, _mm512_srli_epi32(total0,4)));
total1 = _mm512_and_epi32(B2, _mm512_add_epi32(total1, _mm512_srli_epi32(total1,4)));
total0 = _mm512_and_epi32(B3, _mm512_add_epi32(total0, _mm512_srli_epi32(total0,8)));
total1 = _mm512_and_epi32(B3, _mm512_add_epi32(total1, _mm512_srli_epi32(total1,8)));
total0 = _mm512_and_epi32(B4, _mm512_add_epi32(total0, _mm512_srli_epi32(total0,16)));
total1 = _mm512_and_epi32(B4, _mm512_add_epi32(total1, _mm512_srli_epi32(total1,16)));
result0 = _mm512_add_epi32(result0,total0);
result1 = _mm512_add_epi32(result1,total1);
}
result0 = _mm512_add_epi32(result0,result1);
result = _mm512_reduce_add_epi32(result0);
return result;
}
vpu_popcount5：
inline uint64_t vpu_popcount5(uint64_t* buf, size_t n) {
_mm_prefetch((const char *)&buf[0], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[8], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[16], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[24], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[32], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[40], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[48], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[56], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[64], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[72], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[80], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[88], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[96], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[104], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[112], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[120], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[128], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[136], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[144], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[152], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[160], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[168], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[176], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[184], _MM_HINT_T1); // vprefetch1
register size_t result;
size_t i;
register const __m512i B0 = _mm512_load_epi32((void*)(magic+0));
register const __m512i B1 = _mm512_load_epi32((void*)(magic+16));
register const __m512i B2 = _mm512_load_epi32((void*)(magic+32));
register const __m512i B3 = _mm512_load_epi32((void*)(magic+48));
register const __m512i B4 = _mm512_load_epi32((void*)(magic+64));
register const __m512i B6 = _mm512_load_epi32((void*)(magic+80));
register __m512i total0;
register __m512i total1;
register __m512i total2;
register __m512i total3;
register __m512i shuf0;
register __m512i shuf1;
register __m512i shuf2;
register __m512i shuf3;
register __m512i result0;
register __m512i result1;
result0 = _mm512_setzero_epi32();
result1 = _mm512_setzero_epi32();
for (i = 0; i < n; i+=32) {
shuf0 = _mm512_load_epi32(&buf[i ]);
shuf1 = _mm512_load_epi32(&buf[i+ 8]);
shuf2 = _mm512_load_epi32(&buf[i+16]);
shuf3 = _mm512_load_epi32(&buf[i+24]);
_mm_prefetch((const char *)&buf[i+192], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+200], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+208], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+216], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+32], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[i+40], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[i+48], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[i+56], _MM_HINT_T0); // vprefetch0
total0 = _mm512_sub_epi32(shuf0, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf0,1))); // max value in nn is 10
total1 = _mm512_sub_epi32(shuf1, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf1,1)));
total2 = _mm512_sub_epi32(shuf2, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf2,1)));
total3 = _mm512_sub_epi32(shuf3, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf3,1)));
total0 = _mm512_add_epi32(_mm512_and_epi32(B1, total0), _mm512_and_epi32(B1,_mm512_srli_epi32(total0,2))); // max value in nnnn is 0100
total1 = _mm512_add_epi32(_mm512_and_epi32(B1, total1), _mm512_and_epi32(B1,_mm512_srli_epi32(total1,2)));
total2 = _mm512_add_epi32(_mm512_and_epi32(B1, total2), _mm512_and_epi32(B1,_mm512_srli_epi32(total2,2)));
total3 = _mm512_add_epi32(_mm512_and_epi32(B1, total3), _mm512_and_epi32(B1,_mm512_srli_epi32(total3,2)));
total0 = _mm512_and_epi32(B2, _mm512_add_epi32(total0, _mm512_srli_epi32(total0,4))); // max value in 0000nnnn is 00001000
total1 = _mm512_and_epi32(B2, _mm512_add_epi32(total1, _mm512_srli_epi32(total1,4)));
total2 = _mm512_and_epi32(B2, _mm512_add_epi32(total2, _mm512_srli_epi32(total2,4)));
total3 = _mm512_and_epi32(B2, _mm512_add_epi32(total3, _mm512_srli_epi32(total3,4)));
total0 = _mm512_add_epi32(total0, total1); // max value in 000nnnnn is 00010000
total1 = _mm512_add_epi32(total2, total3);
total0 = _mm512_add_epi32(total0, _mm512_srli_epi32(total0,8)); // max value in xxxxxxxx00nnnnnn is 00100000
total1 = _mm512_add_epi32(total1, _mm512_srli_epi32(total1,8));
total0 = _mm512_and_epi32(B6, _mm512_add_epi32(total0, _mm512_srli_epi32(total0,16))); // max value in each element is 01000000, i.e. 64
total1 = _mm512_and_epi32(B6, _mm512_add_epi32(total1, _mm512_srli_epi32(total1,16)));
result0 = _mm512_add_epi32(result0,total0);
result1 = _mm512_add_epi32(result1,total1);
}
result0 = _mm512_add_epi32(result0,result1);
result = _mm512_reduce_add_epi32(result0);
return result;
}
答案 0 :(得分：2)
自昨天发布以来，我已经能够在自己的卡上运行您的代码和我的建议。我没有得到与你完全相同的时序，可能是由于我的硬件步进，也许与我的编译器版本有关。但这种趋势仍然存在，我的建议似乎提升了大约15％的性能提升。
我得到了额外的小性能提升，在5％到10％之间，稍微调整一下，如下面的代码所示。请注意，在以下代码段中，B6将每个元素设置为0x000000FF。在这一点上，我认为该算法可能非常接近从GDDR到L2缓存的最大可持续带宽。
（补充说明：这个断言的证明是，如果我用pop循环重复它的popcount5函数的主体十次 - 并注意这是“chunk_size”的十次快速重复输入数据的数量，因此在L2中它会炙手可热九次 - 测试的总时间仅增加了大约五倍，而不是十倍。我提出这个问题是因为我认为你的目标是调整比特计数逻辑的速度，但也许您希望部署它的应用程序实际上有一个更小和/或更热的工作集。如果是这样，DRAM引入的限制 - > L2带宽正在模糊图片。但是请注意，缩小测试输入的大小以使其在L2中保持较热状态似乎会导致其他开销 - 可能是开放式开销 - 变得相对更重要。）
inline uint64_t vpu_popcount5(uint64_t* buf, size_t n) {
_mm_prefetch((const char *)&buf[0], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[8], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[16], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[24], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[32], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[40], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[48], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[56], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[64], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[72], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[80], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[88], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[96], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[104], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[112], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[120], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[128], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[136], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[144], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[152], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[160], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[168], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[176], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[184], _MM_HINT_T1); // vprefetch1
register size_t result;
size_t i;
register const __m512i B0 = _mm512_load_epi32((void*)(magic+0));
register const __m512i B1 = _mm512_load_epi32((void*)(magic+16));
register const __m512i B2 = _mm512_load_epi32((void*)(magic+32));
register const __m512i B6 = _mm512_load_epi32((void*)(magic+80));
register __m512i total0;
register __m512i total1;
register __m512i total2;
register __m512i total3;
register __m512i shuf0;
register __m512i shuf1;
register __m512i shuf2;
register __m512i shuf3;
register __m512i result0;
register __m512i result1;
result0 = _mm512_setzero_epi32();
result1 = _mm512_setzero_epi32();
for (i = 0; i < n; i+=32) {
shuf0 = _mm512_load_epi32(&buf[i ]);
shuf1 = _mm512_load_epi32(&buf[i+ 8]);
shuf2 = _mm512_load_epi32(&buf[i+16]);
shuf3 = _mm512_load_epi32(&buf[i+24]);
_mm_prefetch((const char *)&buf[i+192], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+200], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+208], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+216], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+32], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[i+40], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[i+48], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[i+56], _MM_HINT_T0); // vprefetch0
total0 = _mm512_sub_epi32(shuf0, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf0,1))); // max value in nn is 10
total1 = _mm512_sub_epi32(shuf1, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf1,1)));
total2 = _mm512_sub_epi32(shuf2, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf2,1)));
total3 = _mm512_sub_epi32(shuf3, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf3,1)));
total0 = _mm512_add_epi32(_mm512_and_epi32(B1, total0), _mm512_and_epi32(B1,_mm512_srli_epi32(total0,2))); // max value in nnnn is 0100
total1 = _mm512_add_epi32(_mm512_and_epi32(B1, total1), _mm512_and_epi32(B1,_mm512_srli_epi32(total1,2)));
total2 = _mm512_add_epi32(_mm512_and_epi32(B1, total2), _mm512_and_epi32(B1,_mm512_srli_epi32(total2,2)));
total3 = _mm512_add_epi32(_mm512_and_epi32(B1, total3), _mm512_and_epi32(B1,_mm512_srli_epi32(total3,2)));
total0 = _mm512_and_epi32(B2, _mm512_add_epi32(total0, _mm512_srli_epi32(total0,4))); // max value in 0000nnnn is 00001000
total1 = _mm512_and_epi32(B2, _mm512_add_epi32(total1, _mm512_srli_epi32(total1,4)));
total2 = _mm512_and_epi32(B2, _mm512_add_epi32(total2, _mm512_srli_epi32(total2,4)));
total3 = _mm512_and_epi32(B2, _mm512_add_epi32(total3, _mm512_srli_epi32(total3,4)));
total0 = _mm512_add_epi32(total0, total1); // max value in 000nnnnn is 00010000
total1 = _mm512_add_epi32(total2, total3);
total0 = _mm512_add_epi32(total0, _mm512_srli_epi32(total0,8)); // max value in xxxxxxxx00nnnnnn is 00100000
total1 = _mm512_add_epi32(total1, _mm512_srli_epi32(total1,8));
total0 = _mm512_and_epi32(B6, _mm512_add_epi32(total0, _mm512_srli_epi32(total0,16))); // max value in each element is 01000000, i.e. 64
total1 = _mm512_and_epi32(B6, _mm512_add_epi32(total1, _mm512_srli_epi32(total1,16)));
result0 = _mm512_add_epi32(result0,total0);
result1 = _mm512_add_epi32(result1,total1);
/* Reduce add, which is analogous to SSSE3's PSADBW instruction,
is not implementated as a single instruction in VPUv1, thus
emulated by multiple instructions*/
}
result0 = _mm512_add_epi32(result0,result1);
result = _mm512_reduce_add_epi32(result0);
return result;
}
答案 1 :(得分：1)
请您尝试以下变体，并报告这是否会改善您的表现？我正在解决几个我认为在你的编码中不是最优的问题：
inline uint64_t vpu_popcount3_revised(uint64_t* buf, size_t n) {
_mm_prefetch((const char *)&buf[0], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[8], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[16], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[24], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[32], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[40], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[48], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[56], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[64], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[72], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[80], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[88], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[96], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[104], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[112], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[120], _MM_HINT_T1); // vprefetch1
register size_t result;
size_t i;
register const __m512i B0 = _mm512_load_epi32((void*)(magic+0));
register const __m512i B1 = _mm512_load_epi32((void*)(magic+16));
register const __m512i B2 = _mm512_load_epi32((void*)(magic+32));
register const __m512i B3 = _mm512_load_epi32((void*)(magic+48));
register const __m512i B4 = _mm512_load_epi32((void*)(magic+64));
register __m512i total0;
register __m512i total1;
register __m512i shuf0;
register __m512i shuf1;
register __m512i result0;
register __m512i result1;
result0 = _mm512_setzero_epi32();
result1 = _mm512_setzero_epi32();
for (i = 0; i < n; i+=16) {
shuf0 = _mm512_load_epi32(&buf[i ]);
shuf1 = _mm512_load_epi32(&buf[i+8]);
_mm_prefetch((const char *)&buf[i+128], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+136], _MM_HINT_T1); // vprefetch1
_mm_prefetch((const char *)&buf[i+16], _MM_HINT_T0); // vprefetch0
_mm_prefetch((const char *)&buf[i+24], _MM_HINT_T0); // vprefetch0
total0 = _mm512_sub_epi32(shuf0, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf0,1)));
total1 = _mm512_sub_epi32(shuf1, _mm512_and_epi32(B0, _mm512_srli_epi32(shuf1,1)));
total0 = _mm512_add_epi32(_mm512_and_epi32(B1, total0), _mm512_and_epi32(B1,_mm512_srli_epi32(total0,2)));
total1 = _mm512_add_epi32(_mm512_and_epi32(B1, total1), _mm512_and_epi32(B1,_mm512_srli_epi32(total1,2)));
total0 = _mm512_and_epi32(B2, _mm512_add_epi32(total0, _mm512_srli_epi32(total0,4)));
total1 = _mm512_and_epi32(B2, _mm512_add_epi32(total1, _mm512_srli_epi32(total1,4)));
total0 = _mm512_and_epi32(B3, _mm512_add_epi32(total0, _mm512_srli_epi32(total0,8)));
total1 = _mm512_and_epi32(B3, _mm512_add_epi32(total1, _mm512_srli_epi32(total1,8)));
total0 = _mm512_and_epi32(B4, _mm512_add_epi32(total0, _mm512_srli_epi32(total0,16)));
total1 = _mm512_and_epi32(B4, _mm512_add_epi32(total1, _mm512_srli_epi32(total1,16)));
result0 = _mm512_add_epi32(result0,total0);
result1 = _mm512_add_epi32(result1,total1);
}
/* Reduce add, which is analogous to SSSE3's PSADBW instruction,
is not implementated as a single instruction in VPUv1, thus
emulated by multiple instructions*/
result0 = _mm512_add_epi32(result0,result1);
result = _mm512_reduce_add_epi32(result0);
return result;
}