OMP2012 Flag Description
Cisco Systems Cisco UCS C240 M5 (Intel Xeon Platinum 8280, 2.70 GHz)

Copyright © 2012 Intel Corporation. All Rights Reserved.

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.

• • -GF
  • 

  • This option enables read only string-pooling optimization.

• • -Gf
  • 

  • This option enables read/write string-pooling optimization.

• • -Ob_n
  • 

  • Specifies the level of inline function expansion.

    Ob0 - Disables inlining of user-defined functions. Note that statement functions are always inlined.

    Ob1 - Enables inlining when an inline keyword or an inline attribute is specified. Also enables inlining according to the C++ language.

    Ob2 - Enables inlining of any function at the compiler's discretion.

• • -O2
  • 

  • Enables optimizations for speed. This is the generally recommended optimization level. This option also enables:
    - Inlining of intrinsics
    - Intra-file interprocedural optimizations, which include:
    - inlining
    - constant propagation
    - forward substitution
    - routine attribute propagation
    - variable address-taken analysis
    - dead static function elimination
    - removal of unreferenced variables
    - The following capabilities for performance gain:
    - constant propagation
    - copy propagation
    - dead-code elimination
    - global register allocation
    - global instruction scheduling and control speculation
    - loop unrolling
    - optimized code selection
    - partial redundancy elimination
    - strength reduction/induction variable simplification
    - variable renaming
    - exception handling optimizations
    - tail recursions
    - peephole optimizations
    - structure assignment lowering and optimizations
    - dead store elimination
    

    On IA-32 Windows platforms, -O2 sets the following:

    /Og, /Oi-, /Os, /Oy, /Ob2, /GF (/Qvc7 and above), /Gf (/Qvc6 and below), /Gs, and /Gy.

  • Includes:
    • -Oi-
    • -Gs
    • -Oy
    • -Gy
    • -Os
    • -GF
    • -Gf
    • -Ob_n
    • -Og
    • -O1
      • -unroll_n
      • -Oi-
      • -Op-
      • -Oy
      • -Gy
      • -Os
      • -GF
      • -Gf
      • -Ob_n
      • -Og
• • -Oi-
  • 

  • Disables inline expansion of all intrinsic functions.

• • -Gs
  • 

  • This option disables stack-checking for routines with 4096 bytes of local variables and compiler temporaries.

• • -Oy
  • 

  • Allows use of EBP as a general-purpose register in optimizations.

• • -Gy
  • 

  • This option tells the compiler to separate functions into COMDATs for the linker.

• • -Os
  • 

  • This option enables most speed optimizations, but disables some that increase code size for a small speed benefit.

• • -Og
  • 

  • This option enables global optimizations.

• • -O1
  • 

  • Enables optimizations for speed and disables some optimizations that
    increase code size and affect speed.
    To limit code size, this option:
    - Enables global optimization; this includes data-flow analysis, code motion, strength reduction and test replacement, split-lifetime analysis, and instruction scheduling.
    - Disables intrinsic recognition and intrinsics inlining.
    The O1 option may improve performance for applications with very large code size, many branches, and execution time not dominated by code within loops.
    On IA-32 Windows platforms, -O1 sets the following:

    /Qunroll0, /Oi-, /Op-, /Oy, /Gy, /Os, /GF (/Qvc7 and above), /Gf (/Qvc6 and below), /Ob2, and /Og

  • Includes:
    • -unroll_n
    • -Oi-
    • -Op-
    • -Oy
    • -Gy
    • -Os
    • -GF
    • -Gf
    • -Ob_n
    • -Og
• • -unroll_n
  • 

  • Tells the compiler the maximum number of times to unroll loops.

• • -Op-
  • 

  • Disables conformance to the ANSI C and IEEE 754 standards for floating-point arithmetic.

Shell, Environment, and Other Software Settings

Open MP Tuning Flags

Operating System Tuning Parameters

Operating System and Software Tuning Parameters

ulimit -s <n>

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

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.

Free the file system page cache

The command "echo 1> /proc/sys/vm/drop_caches" is used to free up the filesystem page cache.

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 affect 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'

Linux Huge Page settings

In order to take advantage of large pages, your system must be configured to use large pages. 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. (Not necessary on some operating systems like RedHat Enterprise Linux 5.5).

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

On RedHat EL 6 and later, Transparent Hugepages increases the memory page size from 4 kilobytes to 2 megabytes. Transparent Hugepages provides 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.

HUGETLB_MORECORE

Set this environment variable to "yes" to enable applications to use large pages.

KMP_STACKSIZE

Specify stack size to be allocated for each thread.

KMP_AFFINITY

KMP_AFFINITY = < physical | logical >, starting-core-id specifies the static mapping of user threads to physical cores. For example, if you have a system configured with 8 cores, OMP_NUM_THREADS=8 and KMP_AFFINITY=physical,0 then thread 0 will mapped to core 0, thread 1 will be mapped to core 1, and so on in a round-robin fashion. KMP_AFFINITY = granularity=fine,scatter The value for the environment variable KMP_AFFINITY affects how the threads from an auto-parallelized program are scheduled across processors. Specifying granularity=fine selects the finest granularity level, causes each OpenMP thread to be bound to a single thread context. This ensures that there is only one thread per core on cores supporting HyperThreading Technology Specifying scatter distributes the threads as evenly as possible across the entire system. Hence a combination of these two options, will spread the threads evenly across sockets, with one thread per physical core.

OMP_NUM_THREADS

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

Firmware / BIOS / Microcode Settings

Intel Turbo Boost Technology:

Enabling this option allows the processor cores to automatically increase their frequency if they are running below power and temperature, thereby increasing performance. By default, this option is enabled.

Intel Hyper Threading Technology:

Enabling this option allows processor resources to be used more efficiently, enabling multiple threads to run on each core and increasing processor throughput, improving overall performance on threaded software.

Enhanced Intel SpeedStep:

Enabling this option allows the system to dynamically adjust processor voltage and core frequency. This technology can result in decreased average power consumption and decreased average heat production.

Core Multi Processing:

This option specifies the number of logical processor cores that can run on the server. This option sets he state of logical processor cores in a package. If you disable this setting, Hyper Threading is also disabled.

Virtualization Technology:

This option allows the user whether the processor uses Intel Virtualization Technology, which allows a platform to run multiple operating systems and applications in independent partitions. This can be one of the following: Disabled - The processor does not permit virtualization. enabled — The processor allows multiple operating systems in independent partitions. Platform Default — The BIOS option uses the value for this attribute contained in the BIOS defaults for the server type and vendor. By default this BIOS option is enabled.

Direct Cache Access:

Enabling this option allows processors to increase I/O performance by placing data from I/O devices directly into the processor cache. This setting helps to reduce cache misses.

Power Technology:

This BIOS option enables the user to configure the CPU power management settings such as Enhanced Intel SpeedStep, Intel Turbo Boost Technology and Processor Power State C6. Settings in Custom will allow the user to change individual settings for the BIOS parameters in the preceding list. You must select this option if you want to change any of these BIOS parameters. Settings in Energy Efficient will determines the best settings for the BIOS parameters in the preceding list and ignores the individual settings for these parameters. Settings in Disabled state do not perform any CPU power management and any settings for the BIOS parameters in the preceding list are ignored

Processor C1 Enhanced:

Enabling this option allows the processor to transition to its minimum frequency upon entering C1. This setting does not take effect until after you have rebooted the server. In disabled state, the CPU continues to run at its maximum frequency in C1 state. Users should disable this option for performing application benchmarking. In enabled state, the CPU transitions to its minimum frequency. This option saves the maximum amount of power in the C1 state.

Processor State C6:

Enabling this option allows the processor to send the C6 report to the operating system. Users should disable this option for performing application benchmarking.

Energy Performance:

This BIOS option allows you to determine whether system Performance or energy efficiency is more important on server. This can be one of the following: Balanced Energy, Balanced Performance, Energy Efficient and Performance. Balanced Performance optimized to maximum power savings with minimal impact on performance and it is enabled by default. Performance disables all power management options with any impact on performance. Balanced Energy is optimized for power efficiency and "Energy Efficient" for power savings. The BIOS option is only selectable if “Power Technology" is set to "Custom".

CPU Performance:

This BIOS option allows the enabling/disabling of a processor mechanism in 3 modes: Enterprise, High-Throughput and HPC. Setting this BIOS option in Enterprise and High-Throughput modes, will enable all the prefetchers and disable Data Reuse Technology. Setting this BIOS option in HPC mode will enable all the prefetchers and enable Data Reuse Technology.

LLC Prefetch:

This BIOS option configures the processor last level cache (LLC) prefetch feature as a result of the non-inclusive cache architecture. The LLC prefetcher exists on top of other prefetchers that can prefetch data into the core data cache unit (DCU) and mid-level cache (MLC). In some cases, setting this option to disabled can improve performance. Values for this BIOS option can be: Disabled: Disables the LLC prefetcher. The other core prefetchers are unaffected. Enabled: Gives the core prefetcher the ability to prefetch data directly to the LLC. By default, LLC prefetch option is disabled.

Power Performance Tuning:

This BIOS option determines how aggressively the CPU will be power managed and placed into turbo. With “BIOS Controls”, the system controls the setting. Selecting "OS Controls” allows the operating system to control it.

Memory Power Saving Mode:

This BIOS option controls the DIMM power savings mode policy. Setting this BIOS option in Disabled, DIMMs do not enter power saving mode. Setting this BIOS option in Slow, DIMMs can enter power saving mode, but the requirements are higher. Therefore, DIMMs enter power saving mode less frequently. Setting this BIOS option in Fast, DIMMs enter power saving mode as often as possible. Setting this BIOS option in Auto, BIOS controls when a DIMM enters power saving mode based on the DIMM configuration.

LV DDR Mode or Low Voltage DDR Mode and DRAM Clock Throttling:

This BIOS option controls the prioritization of memory operations. Setting this BIOS option in Power-saving-mode will prioritize low voltage memory operations over high frequency memory operations. This mode may lower memory frequency in order to keep the voltage low. Setting this BIOS option in Performance-mode will prioritize high frequency operations over low voltage operations.

Closed Loop Thermal Throttling:

This BIOS option allows the user to enable/disable temperature-based memory throttling. By default this BIOS option is enabled. By enabling this BIOS option, the system BIOS will initiate memory throttling to manage memory performance by limiting bandwidth to the DIMMs, therefore capping the power consumption and preventing the DIMMs from overheating.

Memory RAS Configuration:

This BIOS option allows the user to configure memory reliability, availability and serviceability (RAS). Setting this BIOS option in Maximum Performance, system performance is optimized Setting this BIOS option in Mirroring, system reliability is optimized by using half the system memory as backup. Setting this BIOS option in Lockstep, if the DIMM pairs in the server have an identical type, size, and organization and are populated across the SMI channels, you can enable lockstep mode to minimize memory access latency and provide better performance. Setting this BIOS option in Sparing, system reliability is enhanced with a degree of memory redundancy while making more memory available to the operating system than mirroring.

DRAM Refresh Rate:

This option controls the refresh interval rate for internal memory. By default, the refresh interval rate set as Auto, which is 2X DRAM refresh for every 32ns. Setting this BIOS option in 1X, DRAM cells are refreshed every 64ns.

Patrol Scrub:

This BIOS option is memory RAS feature which runs a background memory scrub against all DIMMs and it can negatively impact performance. By default, this option is enabled. Disabling this option, improves performance.

QPI Snoop Configuration:

There are 4 snoop mode options for how to maintain cache coherency across the Intel QPI fabric, each with varying memory latency and bandwidth characteristics depending on how the snoop traffic is generated.

Cluster on Die (COD) mode logically splits a socket into 2 NUMA domains that are exposed to the OS with half the amount of cores and LLC assigned to each NUMA domain in a socket. This mode utilizes an on-die directory cache and in memory directory bits to determine whether a snoop needs to be sent. Use this mode for highly NUMA optimized workloads to get the lowest local memory latency and highest local memory bandwidth for NUMA workloads.

Home Directory Snoop with OSB is the Opportunistic Snoop Broadcast (OSB) directory mode, the HA could choose to do speculative home snoop broadcast under very lightly loaded conditions even before the directory information has been collected and checked.

In Home Snoop and Early Snoop modes, snoops are always sent , they just originate from different places: the caching agent (earlier) in Early Snoop mode and the home agent (later) in Home Snoop mode.

• Use Home Snoop mode for NUMA workloads that are memory bandwidth sensitive and need both local and remote memory bandwidth.

• Use Early Snoop mode for workloads that are memory latency sensitive or for workloads that benefit from fast cache-to-cache transfer latencies from the remote socket. Snoops are sent out earlier, which is why memory latency is lower in this mode.

Sub Numa Clustering:

This BIOS option provides similar localization benefits as cluster-on-die (COD), without some of COD’s downsides. SNC breaks up the LLC into two disjoint clusters based on address range, with each cluster bound to a subset of the memory controllers in the system. SNC improves average latency to the LLC (last level cache) and memory. SNC is a replacement for the COD feature found in previous processor families. For a multi-socketed system, all SNC clusters are mapped to unique NUMA domains. IMC Interleaving must be set to the correct value to correspond with SNC enable/disable. Values for this BIOS option can be: Disabled: The LLC is treated as one cluster when this option is disabled Enabled: Utilizes LLC capacity more efficiently and reduces latency due to core/IMC proximity. This may provide performance improvement on NUMA-aware operating systems By default this BIOS option set to Disabled.

IMC Interleaving:

This BIOS option controls the interleaving between the Integrated Memory Controllers (IMCs). There are two IMCs per socket in Skylake Server. If IMC Interleaving is set to 2-way, addresses will be interleaved between the two IMCs. If IMC Interleaving is set to 1-way, there will be no interleaving. If SNC is disabled, IMC Interleaving should be set to 2-way. If SNC is enabled, IMC Interleaving should be set to 1-way.

High Bandwidth:

Enabling this option allows the chipset to defer memory transactions and process them out of order for optimal performance.

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. :
  

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 2012-2019 Standard Performance Evaluation Corporation
Tested with SPEC OMP2012 v1.1.
Report generated on Wed May 1 12:07:46 2019 by SPEC OMP2012 flags formatter v538.