void _mm_clflush(void const*_P)

Posted 2022-08-27 rtoax

/**
 * File: _mm_clflush.c
 * Author: Rong Tao <rongtao@????.cn>
 * Date: 2022.05.06
 *
 * _mm_clflush() will flush cacheline if vars in cache.
 *
 * Refs:
 * https://www.codenong.com/52525886/
 * https://zhuanlan.zhihu.com/p/242740319
 */
#include <stdio.h>
#include <stdint.h>

#if defined(__x86_64__)
#include <mmintrin.h>
#include <x86intrin.h>
#else
# error "Not support"
#endif

#ifndef FLUSH
# warning "Define FLUSH test _mm_clflush."
#endif

#define LINE_SIZE   64

#define L1_WAYS     16
#define L1_SETS     64
#define L1_LINES    512

extern void _mm_clflush(void const*_P);

uint8_t data[L1_LINES*LINE_SIZE];

int main(int argc, char *argv[])

        volatile uint8_t *addr;
        register uint64_t i;
        unsigned int junk = 0;
        register uint64_t t1, t2;

        printf("data: %p\\n", data);

        _mm_clflush(data);

        printf("accessing 16 bytes in a cache line:\\n");

        for (i = 0; i < 16; i++) 
                t1 = __rdtscp(&junk);
                addr = &data[i];
                junk = *addr;
                t2 = __rdtscp(&junk) - t1;
#ifdef FLUSH
                /* Flush */
                _mm_clflush(data);
#endif
                printf("i = %2ld, cycles: %ld\\n", i, t2);
        

        return 0;

测试：

[rongtao@localhost mmintrin]$ gcc _mm_clflush.c
_mm_clflush.c:23:3: warning: #warning "Define FLUSH test _mm_clflush." [-Wcpp]
   23 | # warning "Define FLUSH test _mm_clflush."
      |   ^~~~~~~
[rongtao@localhost mmintrin]$ ./a.out
data: 0x404060
accessing 16 bytes in a cache line:
i =  0, cycles: 142
i =  1, cycles: 14
i =  2, cycles: 13
i =  3, cycles: 12
i =  4, cycles: 12
i =  5, cycles: 14
i =  6, cycles: 12
i =  7, cycles: 14
i =  8, cycles: 14
i =  9, cycles: 14
i = 10, cycles: 12
i = 11, cycles: 14
i = 12, cycles: 14
i = 13, cycles: 14
i = 14, cycles: 14
i = 15, cycles: 12
[rongtao@localhost mmintrin]$ gcc _mm_clflush.c -DFLUSH
[rongtao@localhost mmintrin]$ ./a.out
data: 0x404060
accessing 16 bytes in a cache line:
i =  0, cycles: 126
i =  1, cycles: 124
i =  2, cycles: 134
i =  3, cycles: 136
i =  4, cycles: 120
i =  5, cycles: 136
i =  6, cycles: 142
i =  7, cycles: 126
i =  8, cycles: 124
i =  9, cycles: 126
i = 10, cycles: 156
i = 11, cycles: 138
i = 12, cycles: 126
i = 13, cycles: 122
i = 14, cycles: 163
i = 15, cycles: 124