OMP2012 Flag Description
Lenovo Global Technology ThinkSystem SR950

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.

• • -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.

• • -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.

• • -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

Firmware / BIOS / Microcode Settings

Operating Modes Selections: (Default="Efficiency -Favor Performance")

The average customer doesn't know the best way to set each individual power/performance feature for their specific environment. Because of this, a menu option is provided that can help a customer optimize the system for things such as minimum power usage/acoustic levels, maximum efficiency, Energy Star optimization, or maximum performance.

• "Minimal Power" mode strives to minimize the absolute power consumption of the system while it is operating. The tradeoff is that performance may be reduced in this mode depending on the application that is running.
• "Efficiency -Favor Power" mode maximizes the performance/watt efficiency with a bias towards power savings. It provides the best features for reducing power and increasing performance in applications where maximum bus speeds are not critical. It is expected that this will be the favored mode for SPECpower testing. "Efficiency -Favor Power" mode maintains backwards compatibility with systems that included the preset operating modes before Energy Star for servers was released.
• "Efficiency -Favor Performance" mode optimizes the performance/watt efficiency with a bias towards performance. It is the favored mode for Energy Star. Note that this mode is slightly different than "Efficiency -Favor Power" mode. In "Efficiency - Favor Performance" mode, no bus speeds are derated as they are in "Efficiency -Favor Power" mode. "Efficiency -Favor Performance" mode is the default mode.
• "Maximum Performance" mode will maximize the absolute performance of the system without regard for power. In this mode, power consumption is a don't care. Things like fan speed and heat output of the system may increase in addition to power consumption. Efficiency of the system may go down in this mode, but the absolute performance may increase depending on the workload that is running.
• A fifth setting, "Custom", allows the user to individually modify any of the low-level settings that are preset and unchangeable in any of the other 4 preset modes.

C-States:

C-states reduce CPU idle power. There are three options in this mode: Legacy, Autonomous, Disable.

• Legacy: When "Legacy" is selected, the operating system initiates the C-state transitions. For E5/E7 CPUs, ACPI C1/C2/C3 map to Intel C1/C3/C6. For 6500/7500 CPUs, ACPI C1/C3 map to Intel C1/C3 (ACPI C2 is not available). Some OS SW may defeat the ACPI mapping (e.g. intel_idle driver).
• Autonomous: When "Autonomous" is selected, HALT and C1 request get converted to C6 requests in hardware.
• Disable: When "Disable" is selected, only C0 and C1 are used by the OS. C1 gets enabled automatically when an OS autohalts.

C1 Enhanced Mode:

Enabling C1E (C1 enhanced) state can save power by halting CPU cores that are idle.

Turbo Mode:

Enabling turbo mode can boost the overall CPU performance when all CPU cores are not being fully utilized. A CPU core can run above its rated frequency for a short perios of time when it is in turbo mode.

Hyper-Threading:

Enabling Hyper-Threading let operating system addresses two virtual or logical cores for a physical presented core. Workloads can be shared between virtual or logical cores when possible. The main function of hyper-threading is to increase the number of independent instructions in the pipeline for using the processor resources more efficiently.

Execute Disable Bit:

The execute disable bit allows memory to be marked as executable or non-executable when used with a supporting operating system. This can improve system security by configuring the processor to raise an error to the operating system when code attempts to run in non-executable memory.

DCA:

DCA capable I/O devices such as network controllers can place data directly into the CPU cache, which improves response time.

Power/Performance Bias:

Power/Performance bias determines how aggressively the CPU will be power managed and placed into turbo. With "Platform Controlled", the system controls the setting. Selecting "OS Controlled" allows the operating system to control it.

Per Core P-state:

When per-core P-states are enabled, each physical CPU core can operate at separate frequencies. If disabled, all cores in a package will operate at the highest resolved frequency of all active threads.

CPU Frequency Limits:

The maximum turbo frequency can be restricted with turbo limiting to a frequency that is between the maximum turbo frequency and the rated frequency for the CPU installed.

Energy Efficient Turbo:

When energy efficient turbo is enabled, the CPU's optimal turbo frequency will be tuned dynamically based on CPU utilization.

Uncore Frequency Scaling:

When enabled, the CPU uncore will dynamically change speed based on the workload.

MONITOR/MWAIT:

MONITOR/MWAIT instructions are used to engage C-states.

Sub-NUMA Cluster (SNC):

SNC breaks up the last level cache (LLC) into 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 and memory. SNC 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. (See also IMC interleaving.) 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

Snoop Preference:

Select the appropriate snoop mode based on the workload. There are two snoop modes: "HS w. Directory + OSB +HitME cache" and "Home Snoop". Default is "HS w. Directory + OSB +HitME cache".

• HS w. Directory + OSB +HitME cache: Best overall for most workloads.
• Home Snoop: Best for BW sensive workloads.

XPT Prefetcher

XPT prefetch is a mechanism that enables a read request that is being sent to the last level cache to speculatively issue a copy of that read to the memory controller prefetching

UPI Prefetcher

UPI prefetch is a mechanism to get the memroy read started early on DDR bus. The UPI receive path will spawn a memory read to the memory controller prefetcher.

Patrol Scrub:

Patrol Scrub is a memory RAS feature which runs a background memory scrub against all DIMMs. Can negatively impact performance.

DCU Streamer Prefetcher:

DCU (Level 1 Data Cache) streamer prefetcher is an L1 data cache prefetcher. Lightly threaded applications and some benchmarks can benefit from having the DCU streamer prefetcher enabled. Default setting is Enable.

Stale A to S

The in-memory directory has three states: invalid (I), snoopAll (A), and shared (S). Invalid (I) state means the data is clean and does not exist in any other socket`s cache. The snoopAll (A) state means the data may exist in another socket in exclusive or modified state. Shared (S) 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. Values for this BIOS option can be:

• Disabled: Disabling this option allows the feature to process memory directory states as described above.
• 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 A to S may be beneficial in a workload where there are many cross-socket reads.

LLC Dead Line Allocation

In some Intel CPU caching schemes, mid-level cache (MLC) evictions are filled into the last level cache (LLC). If a line is evicted from the MLC to the LLC, the core can flag the evicted MLC lines as "dead." This means that the lines are not likely to be read again. This option allows dead lines to be dropped and never fill the LLC if the option is disabled. Values for this BIOS option can be:

• Disabled: Disabling this option can save space in the LLC by never filling MLC dead lines into the LLC.
• Enabled: Opportunistically fill MLC dead lines in LLC, if space is available.

Adjacent Cache Prefetch:

Lightly threaded applications and some benchmarks can benefit from having the adjacent cache line prefetch enabled. Default is enable.

Intel Virtualization Technology:

Intel Virtualization Technology allows a platform to run multiple operating systems and applications in independent partitions, so that one computer system can function as multiple virtual system. Default is enable.

Acounstic Mode

By using acoustic mode, the user has some control over the fan speeds and airflow (and noise) that is produced by the system fans. This mode can be used for noise or airflow concerns in the user environment. As a result, Mode1,2,3,4,5 increase the possibility that the node might have to be throttled to maintain cooling within the fan speed limitation. If there is power or thermal demanding PCI card installed in the chassis, acoustic mode is automatically disabled.

• None: Fan speeds change as required for optimal cooling
• Mode1: Highest acoustics attenuation (lowest cooling)
• Mode2: Higher acoustics attenuation.
• Mode3: Intermediate acoustics attenuation.
• Mode4: Low acoustics attenuation (higher cooling).
• Mode5: Aggressive cooling 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 2012-2017 Standard Performance Evaluation Corporation
Tested with SPEC OMP2012 v1.0.
Report generated on Thu Nov 2 16:49:32 2017 by SPEC OMP2012 flags formatter v538.