Re: [suse-amd64] sched_setaffinity on Suse 2.6.4/5 (bug in C library)

29 Jun 2004

      Hi again,

Well, looks like a bug in the C library. Using the syscall directly
produces the expected behavior, using the C library produces an error.

Compile the following with -DBUG to see the buggy behavior. Comments?

Phil

#include 
#include 
#include 
#include 
#include 
#include 

void set_affin(void)
{
  int retval;
  cpumask_t mask = { 0 };
                                                                                                   cpu_set(0,mask);
#ifdef BUG
  retval = sched_setaffinity(getpid(),sizeof(cpumask_t),&mask);
#else
  retval =
syscall(__NR_sched_setaffinity,getpid(),sizeof(cpumask_t),&mask);
#endif

  printf("sched_setaffinity returns %d\n",retval);
  if (errno == -1)
    {
      printf("%d ",errno);
      perror("sched_setaffinity");
    }
}

int main(int argc, char **argv)
{
  set_affin();
  sleep(1);
  exit(0);
}

On Tue, 2004-06-29 at 11:51, Philip J. Mucci wrote:
...
Hi folks,
I'm working with some guys at PGI/AMD to get some sched_setaffinity
support in some runtime systems. We're having great difficulty getting
sched_setaffinity working.
The code below was constructed via the code in linux/kernel/sched.c,
contrary to the prototypes and the like. Surely we must be doing
something rather stupid, because we keep getting -EFAULT.
The only thing I can guess is that the sizeof(cpumask) is different in
kernel than it is in user land.
Any help would be greatly appreciated...
Phil
#include 
#include 
#include 
#include 
#include 
void set_affin(void)
{
  cpumask_t mask = { 0, };
  int retval;
cpu_set(1,mask);
  retval = sched_setaffinity(0,sizeof(cpumask_t),&mask);
  printf("sched_setaffinity returns %d, errno %d\n",retval,errno);
  perror("ERROR MESSAGE");
}
                                                                                                 int main(int argc, char **argv)
{
  set_affin();
  sleep(1);
  exit(0);
}