CPU2006 Flag Description
Hewlett-Packard Company ProLiant SL165s G7 (2.30 GHz AMD Opteron 6176)

Compilers: x86 Open64 Compiler Suite

Implicitly Included Flags

This section contains descriptions of flags that were included implicitly by other flags, but which do not have a permanent home at SPEC.

• • -O3
  • 

  • Perform all the optimizations at the -O2 level as well as many more aggressive optimizations. Examples of such aggressive optimizations are loop nest optimizations and generation of prefetch instructions. Although these more aggressive optimizations can significantly speed up the run time execution of the compiled program, in rare cases they may not be profitable and may instead lead to a slow down. Also, some of these more aggressive optimizations may affect the accuracy of some floating point computations.

    If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective. Level 2 is assumed if no value is specified (i.e. "-O". The default is "-O2".

  • Includes:
    • -O2
      • -O1
• • -O2
  • 

  • Perform extensive global optimizations. Examples of such optimizations are control flow optimizations, partial redundancy elimination, and strength reduction. These optimizations can very often reduce the execution time of the compiled program significantly, but they may do so at the expense of increased compilation time. This is the default level of optimization.

    If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective. Level 2 is assumed if no value is specified (i.e. "-O". The default is "-O2".

  • Includes:
    • -O1
• • -O1
  • 

  • Perform minimal local optimizations on sections of straight-line code (basic blocks) only. Examples of such optimizations are instruction scheduling and some peephole optimizations. These optimizations do not usually have any noticeable impact on compilation time.

    If multiple "O" options are used, with or without level numbers, the last such option is the one that is effective. Level 2 is assumed if no value is specified (i.e. "-O". The default is "-O2".

• • -ipa
  • 

  • Instructs the compiler to invoke inter-procedural analysis. Specifying "-ipa" is equivalent to "-IPA" and "-IPA:" with no suboptions, thus the default settings for the individual IPA suboptions are used.

• • -OPT:Ofast
  • 

  • -OPT:Ofast
    Maximizes performance for a given platform using the selected optimizations. "-OPT:Ofast" specifies four optimizations; "-OPT:ro=2", "-OPT:Olimit=0", "-OPT:div_split=ON", and "-OPT:alias=typed". Note the specified optimizations are ordinarily safe but floating point accuracy due to transformations may be diminished.

  • Includes:
    • -OPT:ro
    • -OPT:Olimit
    • -OPT:div_split
    • -OPT:alias
• • -OPT:ro
  • 

  • -OPT:roundoff,ro=(0|1|2|3)
    "-OPT:roundoff" specifies acceptable levels of divergence for both accuracy and overflow/underflow behavior of floating-point results relative to the source language rules. The roundoff value is in the range 0-3 with each value described as follows:
    0 Do no transformations which could affect floating-point results. The default for optimization levels "-O0", "-O1", and "-O2".
    1 Allow all transformations which have a limited affect on floating-point results. For roundoff, limited is defined as only the last bit or two of the mantissa is affected. For overflow or underflow, limited is defined as intermediate results of the transformed calculation may overflow or underflow within a factor of two of where the original expression may have overflowed or underflowed. Note that effects may be less limited when compounded by multiple transformations. This is the default when "-O3" is specified.
    2 Specifies transformations with extensive effects on floating-point results. For example, allow associative rearrangement (i.e. even across loop iterations) and the distribution of multiplication over addition or subtraction. Do not specify transformations known to cause: a. cumulative roundoff errors, or b. overflow/underflow of operands in a large range of valid floating-point values. This is the default when specifying "-OPT:Ofast".
    3 Specify any mathematically valid transformation of floating-point expressions. For example, floating point induction variables in loops are permitted (even if known to cause cumulative roundoff errors). Also permitted are fast algorithms for complex absolute value and divide (which will overflow/underflow for operands beyond the square root of the representable extremes).

• • -OPT:Olimit
  • 

  • -OPT:Olimit=N
    Controls the size of procedures to be optimized. Procedures above the specified cutoff limit, N, are not optimized. N=0 means "infinite Olimit", which causes all procedures to be optimized with no consideration regarding compilation times. Note if "-OPT:Ofast" is enabled then "-OPT:Olimit=0" or when "-O3" is enabled "-OPT:Olimit=9000". The default is "-OPT:Olimit=6000".

• • -OPT:div_split
  • 

  • -OPT:div_split=(on|off|0|1)
    Instruct the compiler to transform x/y into x*(recip(y)). Flags -OPT:Ofast or -OPT:IEEE_arithmetic=3 will enable this optimization. Note this transform generates fairly accurate code. The default is "-OPT:div_split=OFF".

• • -OPT:alias
  • 

  • The "-OPT:" option group controls various optimizations. The "-OPT:" options supersede the defaults that are based on the main optimization level.

    -OPT:alias=<model>
    Identify which pointer aliasing model to use. The compiler will make assumptions during compilation when one or more of the following <model> is specified:

    typed
    Assumes that two pointers of different types will not point to the same location in memory (i.e. the code adheres to the ANSI/ISO C standards). Note when specifying "-OPT:Ofast" turns this option ON.

    (restricted|restrict)
    Assumes that distinct pointers are pointing to distinct non-overlapping objects. The default is that this optimization is disabled.

    disjoint
    Assumes that any two pointer expressions are pointing to distinct non-overlapping objects. This default is that this optimization is disabled.

    ^M field_sensitive
    ^M Replaces the alias algorithm with an alternate implementation that tracks fields of individual pointers, i.e. it is field sensitive. This alternate implementation is also designed to be flow-insensitive, scalable and context-sensitive to heap allocations.

    no_f90_pointer_alias
    Assumes that any two different Fortran 90 pointers are pointing to distinct non-overlapping objects. The default is that this optimization is disabled.

• • -fno-math-errno
  • 

  • Do not set ERRNO after calling math functions that are executed with a single instruction, e.g. sqrt. A program that relies on IEEE exceptions for math error handling may want to use this flag for speed while maintaining IEEE arithmetic compatibility. Note specifying "-Ofast" implies "-fno-math-errno". The default is "-fmath-errno".

• • -ffast-math
  • 

  • "-fast-math" instructs the compiler to relax ANSI/ISO or IEEE rules/specifications for math functions in order to optimize floating-point computations to improve runtime. "-fno-fast-math" instructs the compiler to conform to ANSI and IEEE math rules. This option causes the preprocessor macro __FAST_MATH__ to be defined.
    Note:
    "-Ofast" implies "-ffast-math".
    "-ffast-math" sets options "-fno-math-errno" and "-OPT:IEEE_arithmetic=2".
    "-fno-fast-math" sets options "-fmath-errno" and "-OPT:IEEE arithmetic=1".

Commands and Options Used to Submit Benchmark Runs

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' > run.sh ; numactl --physcpubind=0 bash run.sh"

Shell, Environment, and Other Software Settings

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:

• Create a mount point for the huge pages: "mkdir /mnt/hugepages"
• The huge page file system needs to be mounted when the systems reboots. Add the following to a system boot configuration file before any services are started: "mount -t hugetlbfs nodev /mnt/hugepages"
• Set vm/nr_hugepages=N in your /etc/sysctl.conf file where N is the maximum number of pages the system may allocate.
• Reboot to have the changes take effect.

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

HUGETLB_LIMIT

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".

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.

OMP_NUM_THREADS

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

O64_OMP_AFFINITY_MAP

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

O64_OMP_SPIN_USER_LOCK

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.

LD_LIBRARY_PATH

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.

Operating System Tuning Parameters

OS Tuning

submit= MYMASK=`printf '0x%x' \$((1<<\$SPECCOPYNUM))`; /usr/bin/taskset \$MYMASK $command

When running multiple copies of benchmarks, the SPEC config file feature submit is sometimes used to cause individual jobs to be bound to specific processors. This specific submit command is used for Linux. The description of the elements of the command are:

• /usr/bin/taskset [options] [mask] [pid | command [arg] ... ]:
  taskset is used to set or retreive the CPU affinity of a running process given its PID or to launch a new COMMAND with a given CPU affinity. The CPU affinity is represented as a bitmask, with the lowest order bit corresponding to the first logical CPU and highest order bit corresponding to the last logical CPU. When the taskset returns, it is guaranteed that the given program has been scheduled to a legal CPU.
  
  The default behaviour of taskset is to run a new command with a given affinity mask:
  
  taskset [mask] [command] [arguments]
• $MYMASK: The bitmask (in hexadecimal) corresponding to a specific SPECCOPYNUM. For example, $MYMASK value for the first copy of a rate run will be 0x00000001, for the second copy of the rate will be 0x00000002 etc. Thus, the first copy of the rate run will have a CPU affinity of CPU0, the second copy will have the affinity CPU1 etc.
• $command: Program to be started, in this case, the benchmark instance to be started.

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'

numactl --interleave=all "runspec command"

Launching a process with numactl --interleave=all sets the memory interleave policy so that memory will be allocated using round robin on nodes. When memory cannot be allocated on the current interleave target fall back to other nodes.

Transparent Huge Pages

On RedHat EL 6 and later, Transparent Hugepages increase the memory page size from 4 kilobytes to 2 megabytes. Transparent Hugepages provide significant performance advantages on systems with highly contended resources and large memory workloads. If memory utilization is too high or memory is badly fragmented which prevents hugepages being allocated, the kernel will assign smaller 4k pages instead. Hugepages are used by default if /sys/kernel/mm/redhat_transparent_hugepage/enabled is set to always.

ulimit -s [n | unlimited] (Linux)

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

KMP_STACKSIZE=integer[B|K|M|G|T] (Linux)

Sets the number of bytes to allocate for each parallel thread to use as its private stack. Use the optional suffix B, K, M, G, or T, to specify bytes, kilobytes, megabytes, gigabytes, or terabytes. The default setting is 2M on IA32 and 4M on IA64.

KMP_AFFINITY=physical,n (Linux)

Assigns threads to consecutive physical processors (for example, cores), beginning at processor n. Specifies the static mapping of user threads to physical cores, beginning at processor n. For example, if a system is configured with 8 cores, and OMP_NUM_THREADS=8 and KMP_AFFINITY=physical,2 are set, then thread 0 will mapped to core 2, thread 1 will be mapped to core 3, and so on in a round-robin fashion.

OMP_NUM_THREADS=n

This Environment Variable sets the maximum number of threads to use for OpenMP* parallel regions to n if no other value is specified in the application. This environment variable applies to both -openmp and -parallel (Linux) or /Qopenmp and /Qparallel (Windows). Example syntax on a Linux system with 8 cores:
export OMP_NUM_THREADS=8
Default is the number of cores visible to the OS.

vm.max_map_count-n (Linux)

The maximum number of memory map areas a process may have. Memory map areas are used as a side-effect of calling malloc, directly by mmap and mprotect, and also when loading shared libraries.

Firmware / BIOS / Microcode Settings

Firmware Settings

One or more of the following settings may have been set. If so, the "Platform Notes" section of the report will say so; and you can read below to find out more about what these settings mean.

Power Regulator for ProLiant support (Default=HP Dynamic Power Savings Mode)

Values for this BIOS setting can be:

• HP Dynamic Power Savings Mode: Automatically varies processor speed and power usage based on processor utilization. Allows reducing overall power consumption with little or no impact to performance. Does not require OS support.
• HP Static Low Power Mode: Reduces processor speed and power usage. Guarantees a lower maximum power usage for the system. Performance impacts will be greater for environments with higher processor utilization.
• HP Static High Performance Mode: Processors will run in their maximum power/performance state at all times regardless of the OS power managment policy.
• OS Control Mode: Processors will run in their maximum power/ performance state at all times unless the OS enables' a power management policy.

HP Power Profile (Default = Balanced Power and Performance):

Values for this BIOS setting can be:

• Balanced Power and Performance: Provides the optimum settings to maximize power savings with minimal impact to performance for most Operating Systems and applications.
• Maximum Performance: Disables all power management options that may negatively affect performance.
• Minimum Power Usage: Enables power reduction mechanisms that may negatively affect performance. This mode will guarantee a lower maximum power usage by the system. - Maximum Performance: Disables all power management options that ma negatively affec performance.

Power Efficiency Mode (Default=Efficiency)

Values for this BIOS setting can be:

• Efficiency: Maximize the power efficiency of the server.
• Performance: Maximize the performance of the server.
• Custom: Allows the user to customize power and performance related options individually.

Adjacent Sector Prefetch (Default = Enabled):

This BIOS option allows the enabling/disabling of a processor mechanism to fetch the adjacent cache line within an 128-byte sector that contains the data needed due to a cache line miss.

In some limited cases, setting this option to Disabled may improve performance. In the majority of cases, the default value of Enabled provides better performance. Users should only disable this option after performing application benchmarking to verify improved performance in their environment.

Hardware Prefetch (Default = Enabled):

This BIOS option allows allows the enabling/disabling of a processor mechanism to prefetch data into the cache according to a pattern recognition algorithm.

In some limited cases, setting this option to Disabled may improve performance. In the majority of cases, the default value of Enabled provides better performance. Users should only disable this option after performing application benchmarking to verify improved performance in their environment.

Data Reuse (Default = Enabled):

This BIOS option allows the enabling/disabling of the Data Reuse optimization.

Enabling this option reduces the frequency of L3 cache updates from the L1 cache. This may improve performance by reducing the internal bandwidth consumed by constantly updating L1 cache lines in the L3 cache.

Since this optimization results in more fetches to main memory, in some limited cases, setting this option to Disabled may improve performance. In the majority of cases, the default value of Enabled provides better performance. Users should only disable this option after performing application benchmarking to verify improved performance in their environment.

Thermal Configuration (Default = Optimal Cooling):

This feature allows the user to select the fan cooling solution for the system. Values for this BIOS option can be:

• Optimal Cooling: Provides the most efficient solution by configuring fan speeds to the minimum required to provide adequate cooling.
• Increased Cooling: Will run fans at higher speeds to provide aditional cooling. Increased Cooling should be selected when non-HP storage controllers are cabled to the embedded hard drive cage, or if the system is experiencing thermal issues that cannot be resolved in another manner. This option may also improve performance when Turbo Boost Technology is used.

SATA #1 Controller (Default=Auto)

Sets the mode for the embedded controller. The values for this BIOS setting can be:

• Disabled: Disables SATA controller
• Compatible: Sets controller to IDE Compatiblity mode
• RAID: Sets controller to RAID mode
• AHCI: Sets controller to Advanced Host Controller Interface mode

Flag description origin markings:

	Indicates that the flag description came from the user flags file.
	Indicates that the flag description came from the suite-wide flags file.
	Indicates that the flag description came from a per-benchmark flags file.

For questions about the meanings of these flags, please contact the tester.
For other inquiries, please contact webmaster@spec.org
Copyright 2006-2014 Standard Performance Evaluation Corporation
Tested with SPEC CPU2006 v1.2.
Report generated on Thu Jul 24 03:38:18 2014 by SPEC CPU2006 flags formatter v6906.