thread and cpu it is assigned to

sinu_nayak2001 · 10-14-2009, 07:57 AM

Dear All,

Do we have any function, which when called, will return the cpu number on which the thread --calling the function-- is running.

If this is possible, we can visualize the sceduling of threads.

Thanks and regards,
Srinivas

chrism01 · 10-15-2009, 01:34 AM

http://linux.die.net/man/2/sched_getaffinity followed by CPU_ISSET().

sinu_nayak2001 · 10-15-2009, 08:06 AM

thanks chrism01.

Again I searched the internet, after getting clues from chrism01's answer. I reached at the page,

http://help.lockergnome.com/linux/Al...ict486238.html

This is what I was looking for.

Thanks to David Schwartz for posting the example code on the above thread...I am just siting his code here...

Quote:

Interestingly, recent versions of Linux (with glibc-2.6) have
'sched_getcpu'. It's not particularly useful, but it does exist.

Here's some sample code:

#include <sched.h>
#include <stdio.h>
#include <pthread.h>

void *tf(void *t)
{
int i, j, q, cpu;
for(i=0; i<25600; i++)
for(j=0; j<25600; j++)
{ /* burn some CPU */
q>>=2;
q+=i;
q-=j;
}
cpu=sched_getcpu();
for(i=0; i<25600; i++)
for(j=0; j<25600; j++)
{ /* keep burning */
q<<=2;
q+=i;
}
printf("%d Running on CPU %d\n",
(int) t, cpu);
*(volatile int *) &q=q+1; /* don't let compiler optimize q away */
return (void *) cpu;
}

int main(void)
{ /* create 8 CPU burners and see what CPUs they run on */
pthread_t t[8];
int i;
void *r;
for(i=0; i<8; i++)
pthread_create(&t[i], NULL, tf, (void *) (i+1));
for(i=0; i<8; i++)
pthread_join(t[i], &r);
}

On my quad-core, this is typical:

8 Running on CPU 1
1 Running on CPU 1
4 Running on CPU 3
3 Running on CPU 3
5 Running on CPU 2
6 Running on CPU 0
2 Running on CPU 2
7 Running on CPU 0

DS