O_PATH overhead

/*
 * # perf stat --all-kernel ./open open.c p |&grep -e cycles:khH -e instructions:khH
 *     5,412,222,342      cycles:khH                       #    2.715 GHz
 *     5,878,446,552      instructions:khH                 #    1.09  insn per cycle
 * # perf stat --all-kernel ./open open.c r |&grep -e cycles:khH -e instructions:khH
 *     8,654,592,565      cycles:khH                       #    3.328 GHz
 *     8,223,833,831      instructions:khH                 #    0.95  insn per cycle
 * # perf stat --all-kernel ./open open.c w |&grep -e cycles:khH -e instructions:khH
 *     9,799,845,626      cycles:khH                       #    3.417 GHz
 *     9,059,955,513      instructions:khH                 #    0.92  insn per cycle
 * # perf stat --all-kernel ./open open.c rw |&grep -e cycles:khH -e instructions:khH
 *    10,163,667,588      cycles:khH                       #    3.348 GHz
 *     9,351,841,216      instructions:khH                 #    0.92  insn per cycle
 */

#define _GNU_SOURCE

#include <string.h>
#include <unistd.h>
#include <fcntl.h>

int main(int argc, char *argv[])
{
    char *filename, *mode;
    int fd, flags = O_PATH;

    if (argc < 3)
        return 1;

    filename = argv[1];
    mode = argv[2];

    if (!strcmp(mode, "r"))
        flags = O_RDONLY;
    else if (!strcmp(mode, "w"))
        flags = O_WRONLY;
    else if (!strcmp(mode, "rw"))
        flags = O_RDWR;

    for (int i = 0; i < 1000000; i++) {
        fd = open(filename, flags);
        close(fd);
    }

    return 0;
}