SPEC CPU2017 Flag Description - Platform settings

Operating System Tuning Parameters

sched_cfs_bandwidth_slice_us
When Completely Fair Scheduler bandwidth control is in use, this parameter controls the amount of run-time (bandwidth) transferred to a run queue from the task's control group bandwidth pool. Small values allow the global bandwidth to be shared in a fine-grained manner among tasks, larger values reduce transfer overhead.
The default value is 5000.
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.
Transparent Huge Pages(THP)
This OS option allows 3 options: "always", "madvise", and "never".
THP is an abstraction layer that automates most aspects of creating, managing, and using huge pages. THP is designed to hide much of the complexity in using huge pages from system administrators and developers, as normal huge pages must be assigned at boot time, can be difficult to manage manually, and often require significant changes to code in order to be used effectively. 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. Most recent Linux OS releases have THP enabled by default.
The default value is "always".
tuned-adm profile
This OS setting is used to choose different tunning profiles provided by tuned. The tuning profiles can be divided into two categories: power-saving profiles, and performance-boosting profiles. "powersave" profile is optimize for low power consumption, "throughput-perform" profile is optimized for high throughput to provide excellent performance and "balanced" profile can balance performance and power consumption. The default value is "throughput-performance" in RHEL9.2 or "balanced" in SLES15SP5.

Firmware / BIOS / Microcode Settings

Adjacent Cache Line Prefetch
This BIOS switch allows 2 options: "Enabled" and "Disabled".
This prefetcher always collects cache line pairs (128 bytes) from the main memory, providing that the data is not already contained in the cache. If this prefetcher is disabled, only one cache line (64 bytes) is collected, which contains the data required by the processor.
Default setting is "Enabled".
AES
This BIOS switch allows 2 options: "Enabled" and "Disabled".
This option enables or disables Advanced Encryption Standard (AES) feature. This feature speeds up the process of encrypting information that usess AES.
Default setting is "Enabled".
C states
This BIOS switch allows 2 options: "Enabled" and "Disabled".
This feature enables or disables CPU Power Management feature. This switch allows CPU to go to C-States when it's not 100% ulilized. If this option is disabled, all C-State related features are disabled.
Default setting is "Enabled".
C-State Auto Demotion
This BIOS switch allows 4 options: "Disabled", "C1", "C3" and "C1 and C3". When "C1" is selected, the CPU will conditionally demote C State based on un-cored auto-demote information.
Configure C-State Auto Demotion.
Default setting is "C1 and C3".
C-State Un-demotion
This BIOS switch allows 4 options: "Disabled", "C1", "C3" and "C1 and C3". When "C1" is selected, the CPU will conditionally undemote from demoted C1.
Configure C-State Un-Demotion.
Default setting is "C1 and C3".
CState Pre-Wake
This BIOS switch allows 2 options: "Enabled" and "Disabled".
This feature enables or disables core/package early wake function from deep C-States using core/package C-State Pre-Wake timers.
Default setting is "Enabled".
DMI Max Link Speed
This BIOS switch allows 4 options: "Gen1", "Gen2", "Gen3" and "Gen4".
This feature determines the version of Direct Media Interface (DMI). DMI is an interface between the CPU and southbridge chipset on a computer motherboard.
Default setting is "Gen4".
DDR PowerDown and idle counter
This BIOS switch allows 2 options: "BIOS" and "PCODE".
This feature determines whether BIOS or hardware will control DDR powerdown modes and idle counter. When "PCODE" is selected, hardware algorithm controls the modes. When "BIOS" is selected BIOS controls the modes.
Default setting is "BIOS".
Enhanced C-states
This BIOS switch allows 2 options: "Enabled" and "Disabled".
This feature enables or disables C1E state. If this option is enabled, CPU will switch to minimum speed when all cores enter C-State.
Default setting is "Enabled".
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.
Default setting is "Auto".
Hardware Prefetcher
This BIOS switch allows 2 options: "Enabled" and "Disabled".
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.
Default setting is "Enabled".
Hyper-threading
This BIOS switch 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".
Intel Virtualization Technology
This BIOS switch 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".
Intel(R) Speed Shift Technology
This BIOS switch enables or disables Intel Speed Shif Technology support. If this option is enabled, CPU will operate in a way that with the hardware determined algorism and OS can hand control of the frequency and voltage back to the processor.
Default setting is "Enabled".
Intel(R) Turbo Boost Max Technology 3.0
This BIOS switch allows 2 options: "Enabled" and "Disabled".
Intel Turbo Boost Max Technology 3.0 is a combination of software and hardware coupled with information stored in the processor. It identifies and directs workloads to the fastest core on the die first. Intel Turbo Boost Max Technology 3.0 requires a supported processor and latest Windows 10 x64 – RS5 Edition or later.
Default setting is "Enabled".
Native ASPM
This BIOS switch allows 2 options: "Enabled" and "Disabled".
This feature enables or disables OS to control PCIe Active-state power management (ASPM) features. If this option is enabled, OS will control ASPM feature of PCIe devices.
Default setting is "Enabled".
Package C-State Demotion
This BIOS switch allows 2 options: "Enabled" and "Disabled".
This feature enables or disables Package C-State Demotion for saving power by avoiding multiple transitions from deeper to shallower Package C-State. When OS requestes a shallower Package C-State to CPU in deeper Package C-State, this feature can change it to deeper Package C-State than requested automatically using history information.
Default setting is "Disabled".
Package C-State limit
This BIOS switch allows 7 options: "C0", "C2", "C3", "C6", "C7", "C7S", and "Auto"
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.
Default setting is "Auto".
Package C-State un-demotion
This BIOS switch allows 2 options: "Enabled" and "Disabled".
This feature enables processor to switch back to the original requested deeper Package C-State considering cases where demotion was the incorrect decision in determing Package C-State depth.
Default setting is "Disabled".
Per Core P State OS control mode
This BIOS switch allows 2 options: "Enabled" and "Disabled".
Enable/Disable Per Core P state OS control mode. When this feature is disabled, the highest core request is used for all other core requests.
Default setting is "Enabled".
Race To Halt (RTH)
This BIOS switch allows 2 options: "Enabled" and "Disabled".
RTH will dynamically increase CPU frequency in order to enter Package C-State faster to reduce overall power.
Default setting is "Enabled".
REFRESH_2X_MODE
This BIOS switch allows 3 options: "Disabled", "1- Enabled for WARM or HOT", and "2- Enabled HOT only".
This feature enables REFRESH 2X mode which maintains an acceptable overall error rate by increase DRAM refresh rate when temperature is WARM or HOT. 0 - Disabled. 1 - iMC enables 2xRefresh rate mode when thermal status is Warm or Hot. 2 - iMC enables 2xRefresh rate mode when thermal status is Hot
Default setting is "Disabled".
Total Memory Encryption
This BIOS switch allows 2 options: "Enabled" and "Disabled".
Total Memory Encryption (TME) encrypts all memory data passing to and from the CPU. Intel TME was developed to provide greater protection for system memory against hardware attacks, such as removing and reading the dual in-line memory module (DIMM) after spraying it with liquid gases (cold boot attack) or installing purpose-built attack hardware. Intel TME also helps protect against memory bus probing or relocation/splicing attacks.
Default setting is "Enabled".
VT-d
This BIOS switch 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".