Platform settings file

System and Other Tuning Information

Linux Huge Page settings

In order to take full advantage of using x86 Open64's huge page runtime library, your system must be configured to use huge pages. It is safe to run binaries compiled with "-HP" on systems not configured to use huge pages, however, you will not benefit from the performance improvements huge pages offer. To configure your system for huge pages perform the following steps:

Note that further information about huge pages may be found in your Linux documentation file: /usr/src/linux/Documentation/vm/hugetlbpage.txt

Transparent Huge Pages

The use of transparent huge pages is a feature of some newer Linux distributions which allows huge pages to be allocated and de-allocated automatically without hugetlbfs configuration.

On RHEL 6, the default is to have them enabled. To disable the use of transparent huge pages, do the following:


For the x86 Open64 compiler, the maximum number of huge pages an application is allowed to use can be set at run time via the environment variable HUGETLB_LIMIT. If not set, then the process may use all available huge pages when compiled with "-HP (or -HUGEPAGE)" or a maximum of n pages where the value of n is set via the compile time flag "-HP:limit=n".


This option can be used to select the type of process address space randomization that is used in the system, for architectures that support this feature.

The default varies among distributions. To disable the use address space randomization, do the following:

Using numactl to bind processes and memory to cores

For multi-copy runs or single copy runs on systems with multiple sockets, it is advantageous to bind a process to a particular core. Otherwise, the OS may arbitrarily move your process from one core to another. This can effect performance. To help, SPEC allows the use of a "submit" command where users can specify a utility to use to bind processes. We have found the utility 'numactl' to be the best choice.

numactl runs processes with a specific NUMA scheduling or memory placement policy. The policy is set for a command and inherited by all of its children. The numactl flag "--physcpubind" specifies which core(s) to bind the process. "-l" instructs numactl to keep a process memory on the local node while "-m" specifies which node(s) to place a process memory. For full details on using numactl, please refer to your Linux documentation, 'man numactl'

Note that some versions of numactl, particularly the version found on SLES 10, we have found that the utility incorrectly interprets application arguments as it's own. For example, with the command "numactl --physcpubind=0 -l a.out -m a", numactl will interpret a.out's "-m" option as it's own "-m" option. To work around this problem, a user can put the command to be run in a shell script and then run the shell script using numactl. For example: "echo 'a.out -m a' > ; numactl --physcpubind=0 bash"

ulimit -s <n>

Sets the stack size to n kbytes, or unlimited to allow the stack size to grow without limit.

ulimit -l <n>

Sets the maximum size of memory that may be locked into physical memory.


Sets the maximum number of OpenMP parallel threads auto-parallelized (-apo) applications may use.


Specifies the thread-CPU relationship when the operating system's affinity mechanism is used to assign OpenMP threads to CPUs.


Specifies whether or not to use the user-level spin mechanism for OpenMP locks. If the variable is set to TRUE then user-level spin mechanisms are used. If the variable is set to FALSE then pthread mutexes are used. The default if the variable is not set is the same as FALSE.

powersave -f (on SuSE)

Makes the powersave daemon set the CPUs to the highest supported frequency.

/etc/init.d/cpuspeed stop (on Red Hat)

Disables the cpu frequency scaling program in order to set the CPUs to the highest supported frequency.


An environment variable set to include the x86 Open64 and SmartHeap libraries used during compilation of the binaries. This environment variable setting is not needed when building the binaries on the system under test.