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.
TIA!
Phy
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
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 <[email protected]> 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
>
>
On Sun, Feb 18, 2007 at 09:14:21PM -0800, Phy Prabab wrote:
> 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.
You should ensure that the syscall has really been added to the syscall
table. Their kernel also has a fully working epoll() implementation, but
the syscall is missing from the table. It's a shame because you have to
add a 10-lines patch to enable it again ! It may be the same problem in
your case.
> Thanks!
> Phy
Regards,
Willy
On Sun, 2007-02-18 at 18:02 -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));
int sched_setaffinity(pid_t pid, unsigned int cpusetsize,
cpu_set_t *mask);
sched_setaffinity takes 3 not 2 parameters.
Arjan van de Ven wrote:
> sched_setaffinity takes 3 not 2 parameters.
Yep the interface changed 3 times, hence
it's probably better using the syscall directly.
Search my notes for sched_setaffinity here:
http://www.pixelbeat.org/programming/c_c++_notes.html
P?draig.