Re: Question about setting affinity in 2.4

["Phy Prabab" <phyprabab@gmail.com>]

Willy,

Thanks for the heads up and patch location.  It looks like the guys at
RH seemed to have applied a patch to allow one to set affinity,
however, it might be that it is broken.  Guess I will have to contact
the RH people to get an update as to what they did/did not do.

Thanks!
Phy

On 2/18/07, Willy Tarreau <w@1wt.eu> wrote:
> Hi Phy !
>
> On Sun, Feb 18, 2007 at 06:02:17PM -0800, Phy Prabab wrote:
> > Hello everyone,
> >
> > I am trying to set affinity on a program to make sure I can get the
> > best use of the cache as possible and to eliminate as much noise as
> > possible with running my program.  I have tried unsuccessfully to set
> > affinity using sched_set/getaffinity and the CPU_SET macros.  In
> > particular, I can not seem to get the process to use affinity I
> > specify as in:
> >
> > int main () {
> >  cpu_set_t mask;
> >  cpu_set_t setmask;
> >  long long x;
> >  double foo;
> >  printf("Mask set to %08lx\n", sched_getaffinity(0, &mask));
> >  CPU_SET(1, &mask);
> >  if (sched_setaffinity(0, &mask) == -1) {
> >     printf("error setting affinity.");
> >  }
> >
> >  printf("Mask is reset to %08lx\n", sched_getaffinity(0, &mask));
> >  // do some long lasting calculations ....
> >
> >  return;
> > }
> >
> > No mater what I do, the process is never bond to the processor in
> > question as exposed by this little appy and by cat /proc/<pid>/cpu.
> > Is this just impossible to do?
> >
> > Ah, the kernel I am using is RH 2.4.21-37.ELsmp.
>
> I don't know for RH kernel, but the affinity syscalls are not in 2.4
> mainline. You can apply the patch without much hassle if you want. It's
> in Robert Love's directory :
>
>  http://www.kernel.org/pub/linux/kernel/people/rml/cpu-affinity/v2.4/
>
> I believe you'll have to use an -ac patch for RHEL.
>
> > TIA!
> > Phy
>
> regards,
> Willy
>
>