[Bug libgomp/57298] New: GOMP_CPU_AFFINITY will not work when system has >1024 cores

[sp at numascale dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57298

            Bug ID: 57298
           Summary: GOMP_CPU_AFFINITY will not work when system has >1024
                    cores
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libgomp
          Assignee: unassigned at gcc dot gnu.org
          Reporter: sp at numascale dot com
                CC: jakub at gcc dot gnu.org

Using GOMP_CPU_AFFINITY to set processor affinity on OpenMP threads will not
work if the system has more than 1024 threads.

[root@numa-0 Stream]# OMP_NUM_THREADS=4 GOMP_CPU_AFFINITY=0-3 ./stream.small.x
libgomp: could not get CPU affinity set 


Output from "lscpu" :

[root@numa-0 ~]# lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                1272
On-line CPU(s) list:   0-1271
Thread(s) per core:    1
Core(s) per socket:    6
Socket(s):             212
NUMA node(s):          212
Vendor ID:             AuthenticAMD
CPU family:            16
Model:                 9
Stepping:              1
CPU MHz:               2199.900
BogoMIPS:              4406.00
Virtualization:        AMD-V
L1d cache:             64K
L1i cache:             64K
L2 cache:              512K
L3 cache:              5118K


The issue is that cpu_set_t as defined in /usr/include/sched.h only has room
for 1024 entries when statically allocated. However, libc has support for
allocating dynamic sizes which allows for more than 1024 by using the
CPU_ALLOC() and CPU_FREE() macros.

These files :

libgomp/config/linux/affinity.c
libgomp/config/linux/proc.c
libgomp/config/linux/proc.h

needs to be modified to support systems with > 1024 cores.