Attachment 1471303 Details for Bug 682922 – Sample code that demonstrates fork() delays (unoptimizable by GCC)

Sample code that demonstrates fork() delays (unoptimizable by GCC)

forktest-unoptimizeable.c (text/x-csrc), 1.88 KB, created by xrobau on 2018-07-28 21:28:22 UTC

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Creator: xrobau

Created: 2018-07-28 21:28:22 UTC

Size: 1.88 KB

patch

obsolete

>#include <stddef.h>
>#include <unistd.h>
>#include <stdlib.h>
>#include <stdio.h>
>#include <string.h>
>#include <sys/types.h>
>#include <sys/wait.h>
>#include <sys/time.h>
>
>
>static long numForks = 100;
>
>double doForks() {
>    struct timeval tv_start, tv_end;
>    pid_t child;
>    int i;
>    double diff, val;
>
>    gettimeofday(&tv_start, NULL);
>    for (i = 0; i < numForks; i++) {
>        child = fork();
>        if (child) {
>            waitpid(child, NULL, 0);
>        } else {
>            exit(0);
>        }
>    }
>    gettimeofday(&tv_end, NULL);
>
>    diff = (tv_end.tv_sec * 1000000 + tv_end.tv_usec)
>                       - (tv_start.tv_sec * 1000000 + tv_start.tv_usec);
>    val = ((diff / 1000000) / numForks);
>    return val;
>}
>
>
>int main(int argc, char *argv[]) {
>    volatile int foo;
>
>    printf("Time taken per fork: \t\t%f\n", doForks());
>
>    long mallocSize = 500 * 1024 * 1024;
>    char *p1 = malloc(mallocSize);
>    memset(p1, 0x31,  mallocSize);
>    foo = p1[0]; // volatile
>
>    printf("Time taken with 500MB: \t\t%f\n", doForks());
>
>    char *p2 = malloc(mallocSize);
>    memset(p2, 0x32,  mallocSize);
>    foo = p2[0]; // volatile
>    printf("Time taken with 1GB: \t\t%f\n", doForks());
>
>    char *p3 = malloc(mallocSize);
>    memset(p3, 0x33,  mallocSize);
>    foo = p3[0]; // volatile
>    char *p4 = malloc(mallocSize);
>    memset(p4, 0x34,  mallocSize);
>    foo = p4[0]; // volatile
>    printf("Time taken with 2GB: \t\t%f\n", doForks());
>
>    char *p5 = malloc(mallocSize);
>    char *p6 = malloc(mallocSize);
>    char *p7 = malloc(mallocSize);
>    char *p8 = malloc(mallocSize);
>    memset(p5, 0x35,  mallocSize);
>    memset(p6, 0x36,  mallocSize);
>    memset(p7, 0x37,  mallocSize);
>    memset(p8, 0x38,  mallocSize);
>    foo = p5[0]; // volatile
>    foo = p6[0]; // volatile
>    foo = p7[0]; // volatile
>    foo = p8[0]; // volatile
>
>    printf("Time taken with 4GB: \t\t%f\n", doForks());
>
>    return 0;
>}

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Attachments on bug 682922: 482817 | 941229 | 1471184 | 1471303