CPU2017 Flag Description
Fujitsu PRIMERGY RX2540 M7, Intel Xeon Gold 6458Q, 3.10GHz

Copyright © 2016 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.

• • -O3
  • 

  • Enable O2 optimizations plus more aggressive optimizations, such as prefetching, scalar replacement, and loop and memory access transformations. Enable optimizations for maximum speed, such as:

    • Loop unrolling, including instruction scheduling
    • Code replication to eliminate branches
    • Padding the size of certain power-of-two arrays to allow more efficient cache use.
    
    

    On IA-32 and Intel EM64T processors, when O3 is used with options -ax or -x (Linux) or with options /Qax or /Qx (Windows), the compiler performs more aggressive data dependency analysis than for O2, which may result in longer compilation times. The O3 optimizations may not cause higher performance unless loop and memory access transformations take place. The optimizations may slow down code in some cases compared to O2 optimizations. The O3 option is recommended for applications that have loops that heavily use floating-point calculations and process large data sets.

  • Includes:
    • -O2
      • -O1
        • -funroll-loops
        • -fno-builtin
        • -mno-ieee-fp
        • -fomit-framepointer
        • -ffunction-sections
        • -ftz
• • -O2
  • 

  • Enable 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
    

  • Includes:
    • -O1
      • -funroll-loops
      • -fno-builtin
      • -mno-ieee-fp
      • -fomit-framepointer
      • -ffunction-sections
      • -ftz
• • -O1
  • 

  • Enable optimizations for speed and disables some optimizations that increase code size and affect speed.
    To limit code size, this option:

    • Enable 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.

    -O1 sets the following options:
    -funroll-loops0, -fno-builtin, -mno-ieee-fp, -fomit-framepointer, -ffunction-sections, -ftz
  • Includes:
    • -funroll-loops
    • -fno-builtin
    • -mno-ieee-fp
    • -fomit-framepointer
    • -ffunction-sections
    • -ftz
• • -funroll-loops
  • 

  • Tells the compiler the maximum number of times to unroll loops. For example -funroll-loops0 would disable unrolling of loops.

• • -fno-builtin
  • 

  • -fno-builtin disables inline expansion for all intrinsic functions.

• • -mno-ieee-fp
  • 

  • This option trades off floating-point precision for speed by removing the restriction to conform to the IEEE standard.

• • -fomit-framepointer
  • 

  • EBP is used as a general-purpose register in optimizations.

• • -ffunction-sections
  • 

  • Places each function in its own COMDAT section.

• • -ftz
  • 

  • Flushes denormal results to zero.

Commands and Options Used to Submit Benchmark Runs

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 used to cause individual jobs to be bound to specific processors. This specific submit command, using taskset, is used for Linux64 systems without numactl.
Here is a brief guide to understanding the specific command which will be found in the config file:

• /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 specific, legal CPU, as defined by the mask setting.
• [mask]: The bitmask (in hexadecimal) corresponding to a specific SPECCOPYNUM. The specific example above, computes this mask value in the variable $MYMASK. The value of this mask 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.

submit= numactl --localalloc --physcpubind=$SPECCOPYNUM $command

When running multiple copies of benchmarks, the SPEC config file feature submit is used to cause individual jobs to be bound to specific processors. This specific submit command is used for Linux64 systems with support for numactl.
Here is a brief guide to understanding the specific command which will be found in the config file:

• syntax: numactl [--interleave=nodes] [--preferred=node] [--physcpubind=cpus] [--cpunodebind=nodes] [--membind=nodes] [--localalloc] command args ...
• 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.
• "--localalloc" instructs numactl to keep a process memory on the local node while "-m" specifies which node(s) to place a process memory.
• "--physcpubind" specifies which core(s) to bind the process. In this case, copy 0 is bound to processor 0 etc.
• For full details on using numactl, please refer to your Linux documentation, 'man numactl'

Shell, Environment, and Other Software Settings

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.

KMP_STACKSIZE

Specify stack size to be allocated for each thread.

KMP_AFFINITY

Syntax: KMP_AFFINITY=[<modifier>,...]<type>[,<permute>][,<offset>]
The value for the environment variable KMP_AFFINITY affects how the threads from an auto-parallelized program are scheduled across processors.
It applies to binaries built with -qopenmp and -parallel (Linux and Mac OS X) or /Qopenmp and /Qparallel (Windows).
modifier:
    granularity=fine Causes each OpenMP thread to be bound to a single thread context.
type:
    compact Specifying compact assigns the OpenMP thread <n>+1 to a free thread context as close as possible to the thread context where the <n> OpenMP thread was placed.
    scatter Specifying scatter distributes the threads as evenly as possible across the entire system.
permute: The permute specifier is an integer value controls which levels are most significant when sorting the machine topology map. A value for permute forces the mappings to make the specified number of most significant levels of the sort the least significant, and it inverts the order of significance.
offset: The offset specifier indicates the starting position for thread assignment.

Please see the Thread Affinity Interface article in the Intel Composer XE Documentation for more details.

Example: KMP_AFFINITY=granularity=fine,scatter
Specifying granularity=fine selects the finest granularity level and causes each OpenMP or auto-par 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.

Example: KMP_AFFINITY=compact,1,0
Specifying compact will assign the n+1 thread to a free thread context as close as possible to thread n.
A default granularity=core is implied if no granularity is explicitly specified.
Specifying 1,0 sets permute and offset values of the thread assignment.
With a permute value of 1, thread n+1 is assigned to a consecutive core. With an offset of 0, the process's first thread 0 will be assigned to thread 0.
The same behavior is exhibited in a multisocket system.

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 -qopenmp 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

Set stack size to unlimited

The command "ulimit -s unlimited" is used to set the stack size limit to unlimited.

Free the file system page cache

The command "echo 3> /proc/sys/vm/drop_caches" is used to free up the filesystem page cache as well as reclaimable slab objects like dentries and inodes.

Red Hat Specific features

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 unless the /sys/kernel/mm/redhat_transparent_hugepage/enabled field is changed from its RedHat EL6 default of 'always'.

Operating System Tuning Parameters

cpupower frequency-set

cpupower utility is a collection of tools for power efficiency of processor. frequency-set sub-command controls settings for processor frequency. "-g [governor]" specifies a policy to select processor frequency. The performance governor statically sets frequency of the processor cores specified by "-c" option to the highest possible for maximum performance.

cpupower idle-set

idle-set sub-command of cpupower utility controls a processor idle state (C-state) of the kernel. "-d [state_no]>" option disables a specific processor idle state. Disabling idle state can reduce the idle-wakeup delay, but it results in substantially higher power consumption. By default, processor idle states of all CPU cores are set.

irqbalance

Disabled through "service irqbalance stop". Depending on the workload involved, the irqbalance service reassigns various IRQ's to system CPUs. Though this service might help in some situations, disabling it can also help environments which need to minimize or eliminate latency to more quickly respond to events.

isolcpus

This kernel option excludes a specified processor from load balancing by the kernel scheduler. This prevents the scheduler from scheduling any user-space threads on this processor.

nohz_full

This kernel option sets adaptive tick mode (NOHZ_FULL) to specified processors. Since the number of interrupts is reduced to ones per second, latency-sensitive applications can take advantage of it.

numa_balancing

This OS setting controls automatic NUMA balancing on memory mapping and process placement. Setting 0 disables this feature. It is enabled by default (1).

sched_latency_ns

This OS setting configures targeted preemption latency for CPU bound tasks. The default value is 24000000 (ns).

sched_migration_cost_ns

Amount of time after the last execution that a task is considered to be "cache hot" in migration decisions. A "hot" task is less likely to be migrated to another CPU, so increasing this variable reduces task migrations. The default value is 500000 (ns).

sched_min_granularity_ns

This OS setting controls the minimal preemption granularity for CPU bound tasks. As the number of runnable tasks increases, CFS(Complete Fair Scheduler), the scheduler of the Linux kernel, decreases the timeslices of tasks. If the number of runnable tasks exceeds sched_latency_ns/sched_min_granularity_ns, the timeslice becomes number_of_running_tasks * sched_min_granularity_ns. The default value is 10000000(ns).

sched_wakeup_granularity_ns

This OS setting controls the wake-up preemption granularity. Increasing this variable reduces wake-up preemption, reducing disturbance of compute bound tasks. Lowering it improves wake-up latency and throughput for latency critical tasks, particularly when a short duty cycle load component must compete with CPU bound components. The default value is 15000000 (ns).

Firmware / BIOS / Microcode Settings

Adjacent Cache Line Prefetch

This BIOS switch allows 2 options: "Disabled" and "Enabled". The default is "Enabled".

Available if the processor offers a mechanism for loading an additional adjacent 64 Byte cache line during every cache request of the processor. This will increase cache hit ratio for applications with high spatial locality.

AVX P1

This BIOS switch allows 3 options: "Normal", "Level1" and "Level2". The default is "Normal".

Enables you to reconfigure the processor Thermal Design Power (TDP) levels during POST based on the power and thermal delivery capabilities of the system. TDP verifies the maximum heat the cooling system is must dissipate. This option is set to Normal by default.

CPU C1E Support

Enabling this option which is the default allows the processor to transmit to its minimum frequency when entering the power state C1. If the switch is disabled the CPU stays at its maximum frequency in C1. Because of the increase of power consumption users should only select this option after performing application benchmarking to verify improved performance in their environment.

CPU Performance Boost

This BIOS switch allows 3 options: "Disabled", "Moderate", and "Aggressive". The default is "Disabled"

This switch enables CPU performance boost feature which improves CPU performance at the cost of additional power consumption. Setting this option to "Moderate" improves some CPU performance but consumes higher power. Setting this option to "Aggressive" achieves the highest CPU performance but consumes even higher power than "Moderate" setting.

DBP-F

This BIOS switch allows 2 options: "Enabled" and "Disabled". The default is "Disabled".

DBP-F is a new feature that can benefit multi-threaded workloads, but workloads that are single-threaded could experience lower performance.

DCU Ip Prefetcher

This BIOS switch allows 2 options: "Enabled" and "Disabled". The default is "Enabled".

This L1-cache prefether looks for sequential load history and attempts on this basis to determine the next data to be expected and, if necessary, to prefetch this data from the L2 cache or the main memory into the L1 cache.

DCU Streamer Prefetcher

This BIOS switch allows 2 options: "Enabled" and "Disabled". The default is "Enabled".

This prefetcher is a L1 data cache prefetcher, which detects multiple loads from the same cache line done within a time limit, in order to then prefetch the next line from the L2 cache or the main memory into the L1 cache based on the assumption that the next cache line will also be needed.

Energy Performance

This BIOS switch allows 4 options: "Balanced performance", "Performance", "Balanced Energy" and "Energy Efficient". The default is "Performance" optimized to maximum power savings with minimal impact on performance. "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 switch is only selectable if the BIOS switch "Power Technology" is selectable and set to "Custom".

The two options "Balanced Performance" and "Balanced Energy" should always be the first choice as both options optimize the efficiency of the system. In cases where the performance is not sufficient or the power consumption is too high the two options "Performance" or "Energy Efficient" could be an alternative.

Fan Control

This BIOS switch allows 2 options: "Auto" and "Full". The default setting is "Auto", which allows the system to control the fan speed according to the system temperature. If "Full" is selected, the system runs fans at 100% speed and it may improve the system performance. But it increases the power consumption of the system.

Intel Virtualization Technology

This BIOS option enables or disables additional virtualization functions of the CPU. If the server is not used for virtualization, this option should be set to "Disabled". This can result in energy savings. Default setting is "Enabled".

Hardware Prefetcher

This BIOS switch allows 2 options: "Enabled" and "Disabled". The default is "Enabled".

This prefetcher looks for data streams on the assumption that if the data is requested at address A and A+1, the data will also presumably be required at address A+2. This data is then prefetched into the L2 cache from the main memory.

Homeless Prefetch

This BIOS switch allows 3 options: "Auto","Enabled", and "Disabled". The default is "Auto".

This prefetcher allows L1 Data Cache Unit (DCU) to prefetech when the Fill Buffers (FB) is full and it may reduce the latency in some workloads.

HWPM Support

This BIOS switch allows 4 options: "Native Mode", "Disabled", "OOB Mode" and "Native Mode with no legacy". The default is "Native Mode".

With Hardware Power Management(HWPM) the processors provides a flexible interface between Hardware and Platform for performance management and improving energy efficiency.

In Native Mode the HWPM operates cooperatively with the OS via a software interface to provide constraints and hints.

When disabled, system does not use HWPM.

Hyper-Threading

This BIOS option enables or disables additional hardware thread which shares same physical core. Generally "Enabled" is recommended but disabling it makes sense for the application which requires the shortest possible response times. Default setting is "Enabled".

LLC Dead Line Alloc

This BIOS switch allows 2 options: "Enabled" and "Disabled". The default is "Enabled". In the Cascadelake non-inclusive cache scheme, the mid-level cache (MLC) evictions are filled into the last-level cache (LLC). When lines are evicted from the MLC, the core can flag them as "dead" (i.e., not likely to be read again). The LLC has the option to drop dead lines and not fill them in the LLC. If the Dead Line LLC Alloc feature is disabled, dead lines will always be dropped and will never fill into the LLC. This can help save space in the LLC and prevent the LLC from evicting useful data. However, if the Dead Line LLC Alloc feature is enabled, the LLC can opportunistically fill dead lines into the LLC if there is free space available.

LLC Prefetch

This BIOS switch allows 2 options: "Enabled" and "Disabled". The default is "Disabled".

This 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. Typically, setting this option to enable provides better performance. If this prefetcher is enabled, the core can prefetch data directly to the LLC and if disabled, the other core prefetchers are unaffected.

Optimized Power Mode

This BIOS switch allows 2 options: "Enabled" and "Disabled". The default is "Disabled"

This switch enables Optimized Power Mode which is CPU energy efficiency mode and is optimized to reduce CPU power under low workload.

Override OS Energy Performance

This BIOS switch allows 2 options: "Enabled" and "Disabled". The default is "Disabled". The power control unit (PCU) in the processors takes on the central role of controlling the energy-saving options. The PCU can be parameterized in order to consequently control the settings more in the direction of energy efficiency or in the direction of maximum performance. The default setting allows you to control energy-saving options through the operating system by its power plan. If enabled, PCU overrides the setting of the operating system and controls the energy-saving options based on the settings in the BIOS.

Package C State limit

This BIOS option allows 5 options: "C0", "C2", "C6", "C6(Retention)"and "No Limit". The default setting is "C6". Package C-states is one of energy-saving options of the processor, which not only allow the individual cores of a processor, but the entire processor chip to be put into a type of sleep state. As a result, power consumption is even further reduced. But the "waking-up time" that is required to change from the lower package C-states to the active (C0) state is even longer in comparison with the CPU or core C-states. If the "C0" setting is made in the BIOS, the processor chip always remains active. It can improve the performance of latency sensitive workloads.

Patrol Scrub

This BIOS option enables or disables the so-called memory scrubbing, which cyclically accesses the main memory of the system in the background regardless of the operating system in order to detect and correct memory errors in a preventive way. The time of this memory test cannot be influenced and can under certain circumstances result in losses in performance. The disabling of the Patrol Scrub option increases the probability of discovering memory errors in case of active accesses by the operating system. Until these errors are correctable, the ECC technology of the memory modules ensures that the system continues to run in a stable way. However, too many correctable memory errors increase the risk of discovering non-correctable errors, which then result in a system standstill.

RdCur for XPT Prefetch

This BIOS switch allows 3 options: "Auto", "Enable" and "Disable". The default is "Auto".

Enable-Set the suppress_mem_rd_prefetch_rdcur. Disable-Reset it. Auto-Auto decides based on Si Compatibility.

SNC (Sub NUMA)

Sub NUMA Clustering (SNC) breaks up the last-level cache (LLC) into two disjoint clusters based on address range, with each cluster bound to one memory controller. SNC improves average latency to the LLC/memory and is a replacement for the "Cluster On Die" (COD) feature found in previous processor families. For a multi-socketed system, all SNC clusters are mapped to unique NUMA domains. The BIOS switch "SNC (Sub NUMA)" allows 3 options: "Enable SNC2", "Enable SNC4" and "Disabled". The default setting is "Disabled"

Stale AtoS (Directory AtoS)

This BIOS switch allows 3 options: "Enabled", "Disabled" and "Auto". The default is "Auto".

The in-memory directory has three states: I, A, and S. I (invalid) state means the data is clean and does not exist in any other socket's cache. A (snoopAll) state means the data may exist in another socket in exclusive or modified state. S (Shared) state means the data is clean and may be shared across one or more socket's caches.

When doing a read to memory, if the directory line is in the A state we must snoop all the other sockets because another socket may have the line in modified state. If this is the case, the snoop will return the modified data. However, it may be the case that a line is read in A state and all the snoops come back a miss. This can happen if another socket read the line earlier and then silently dropped it from its cache without modifying it.

If Stale AtoS feature is enabled, in the situation where a line in A state returns only snoop misses, the line will transition to S state. That way, subsequent reads to the line will encounter it in S state and not have to snoop, saving latency and snoop bandwidth. Stale AtoS may be beneficial in a workload where there are many cross-socket reads.

Uncore Frequency Scaling

This BIOS switch allows 3 options: "Auto", "Power Balanced" and "Maximum". The default is "Auto" which ensures that the uncore frequency is regulated by CPU itself. "Maximum" sets the uncore frequency to the fixed maximum uncore frequency available.

The option "Maximum" may improve performance but also increase the power consumption of the system. Users should only select this option after performing application benchmarking to verify improved performance in their environment.

UPI Link Frequency Select

This switch allows the configuration of the Intel Ultra Path Interconnect (UPI) link speed. Default is auto, which configures the optimal link speed automatically. It can be set "12.8 GT/s", "14.4 GT/s", "16.0 GT/s" or "Auto".

UPI Link L0p

This BIOS switch allows 2 options: "Disabled" and "Enabled". The default setting is "Enabled".

This switch enables or disables Intel Ultra Path Interconnect (UPI) link L0p state for power saving.

UPI Link L1

This BIOS switch allows 2 options: "Disabled" and "Enabled". The default setting is "Enabled".

This switch Specifies whether the UPI L1 power state can be used on the links between the CPUs, to reduce the power consumption.

Utilization Profile

This BIOS switch allows 2 options: "Even" and "Unbalanced". The default is "Even" and the best choice for all workloads utilizing the whole system. In cases where the utilization is highly concentrated on few resources of the system the performance of the application could be improved by setting to "Unbalanced".

Setting this option to "Unbalanced" may improve performance but also increase the power consumption of the system. Users should only select this option after performing application benchmarking to verify improved performance in their environment.

VT-d

This BIOS option enables or disables I/O virtualization functions of the CPU. If the server is not used for virtualization, this option should be set to "Disabled". Default setting is "Enabled".

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 info@spec.org
Copyright 2017-2023 Standard Performance Evaluation Corporation
Tested with SPEC CPU2017 v1.1.9.
Report generated on 2023-06-20 23:26:52 by SPEC CPU2017 flags formatter v5178.