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ensure context switch always happen #59

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ensure context switch always happen #59

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34 changes: 34 additions & 0 deletions UnixBench/src/context1.c
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,9 @@ char SCCSid[] = "@(#) @(#)context1.c:3.3 -- 5/15/91 19:30:18";
*
*/

#define _GNU_SOURCE
#include <sched.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
Expand All @@ -37,6 +40,10 @@ void report()
exit(0);
}

static int get_cpu_num(void){
return sysconf(_SC_NPROCESSORS_ONLN);
}

int main(argc, argv)
int argc;
char *argv[];
Expand All @@ -45,6 +52,7 @@ char *argv[];
unsigned long check;
int p1[2], p2[2];
ssize_t ret;
int need_affinity;

if (argc != 2) {
fprintf(stderr, "Usage: context duration\n");
Expand All @@ -53,6 +61,14 @@ char *argv[];

duration = atoi(argv[1]);

/* if os has more than one cpu, will bind parent process to cpu 0 and child process to other cpus
* In this way, we can ensure context switch always happen
* */
if (get_cpu_num() > 1)
need_affinity = 1;
else
need_affinity = 0;

/* set up alarm call */
iter = 0;
wake_me(duration, report);
Expand All @@ -64,6 +80,16 @@ char *argv[];
}

if (fork()) { /* parent process */
if (need_affinity) {
cpu_set_t pmask;
CPU_ZERO(&pmask);
CPU_SET(0, &pmask);
if (sched_setaffinity(0, sizeof(cpu_set_t), &pmask) == -1)
{
perror("parent sched_setaffinity failed");
}
}

/* master, write p1 & read p2 */
close(p1[0]); close(p2[1]);
while (1) {
Expand Down Expand Up @@ -94,6 +120,14 @@ char *argv[];
}
}
else { /* child process */
if (need_affinity) {
cpu_set_t cmask;
if (sched_getaffinity(0, sizeof(cpu_set_t), &cmask) != -1) {
CPU_CLR(0, &cmask);
if (sched_setaffinity(0, sizeof(cpu_set_t), &cmask) == -1)
perror("child sched_setaffinity failed");
}
}
/* slave, read p1 & write p2 */
close(p1[1]); close(p2[0]);
while (1) {
Expand Down