SPEC CPU2017 Flag Description - Platform settings

Operating System Tuning Parameters

ulimit

This sets user limits of system-wide resources and can set the stack size to n kbytes, or unlimited to allow the stack size to grow without limit. Some common ulimit commands may include:

ulimit -s [n | unlimited]: Set the stack size to n kbytes, or unlimited to allow the stack size to grow without limit.
ulimit -l (number): Set the maximum size that can be locked into memory.

Kernel parameters

The following Linux Kernel parameters were set for better optimize performance.

dirty_ratio: Set through "echo 8 > /proc/sys/vm/dirty_ratio". This setting is the absolute maximum amount of system memory that can be filled with dirty pages before everything must get committed to disk.
swappiness: The swappiness value can range from 1 to 100. A value of 100 will cause the kernel to swap out inactive processes frequently in favor of file system performance, resulting in large disk cache sizes. A value of 1 tells the kernel to only swap processes to disk if absolutely necessary. This can be set through a command like "echo 1 > /proc/sys/vm/swappiness"
zone reclaim mode: Zone reclaim allows the reclaiming of pages from a zone if the number of free pages falls below a watermark even if other zones still have enough pages available. Reclaiming a page can be more beneficial than taking the performance penalties that are associated with allocating a page on a remote zone, especially for NUMA machines. To tell the kernel to free local node memory rather than grabbing free memory from remote nodes, use a command like "echo 1 > /proc/sys/vm/zone_reclaim_mode"
Free the file system page cache: The command "echo 1> /proc/sys/vm/drop_caches" is used to free up the filesystem page cache.

Firmware / BIOS / Microcode Settings

ACPI _CST C1 Declaration

This BIOS switch allows 3 options: "Disabled", "Enabled", and "Auto". This feature determines whether or not to declare the C1 state to OS. Default is Auto.

cTDP

Configures the maximum power that the CPU will consume, up to the platform power limit. Valid values vary by CPU model. If value outside the valid range is set, the CPU will automatically adjust the value so that it does fall within the valid range. When increasing cTDP, additional power will only be consumed up to the Package Power Limit, which may be less than the cTDP setting.

Model	Minimum cTDP	Maximum cTDP
EPYC 7502	180	200
EPYC 7452	155	180
EPYC 7402	180	200
EPYC 7352	155	180
EPYC 7302	155	180
EPYC 7282	120	150
EPYC 7262	155	180
EPYC 7252	120	150

Determinism Slider

This BIOS switch allows 3 options: "Auto", "Power", and "Performance". This feature is for the determinism to control performance. "Auto" setting uses default values for deterministic performance control. "Power" setting provides predicable performance across all processors of the same type. "Power" setting maximizes performance withing the power limits defined by cTDP. Default is "Auto".

DRAM Scrub Time

This feature controls the time between DRAM 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. This BIOS switch allows 8 options: "Disabled", "1 hour", "4 hours", "8 hours", "16 hours", "24 hours", "48 hours", and "Auto". "Disabled" option disables the feature of DRAM Scrubbing and it may result in improving the performance under certain circumstances but 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.

Global C-state Control

This BIOS switch allows 2 options: "Disabled", "Enabled, and "Auto". This feature controls IO based C-state generation and DF C-states. Default is "Auto"

L1 Stream HW Prefetcher

This BIOS switch allows 2 options: "Disabled", "Enabled, and "Auto". This feature allows enabling or disabling of L1 Stream HW Prefetcher. Auto. Default is "Auto".

L2 Stream HW Prefetcher

This BIOS switch allows 2 options: "Disabled", "Enabled, and "Auto". This feature allows enabling or disabling of L2 Stream HW Prefetcher. Default is "Auto".

NUMA nodes per socket

This BIOS switch allows 5 options: "NPS0", "NPS1", "NPS2", "NPS4", and "Auto". This feature specifies the number of desired NUMA nodes per populated socket in the system:

NPS0: All physical processor is a NUMA node and memory accesses are interleaved across all memory channels of two sockets together.
NPS1: Each physical processor is a NUMA node, and memory accesses are interleaved across all memory channels directly connected to the physical processor.
NPS2: Each physical processor is two NUMA nodes, and memory accesses are interleaved across 4 memory channels.
NPS4: Each physical processor is four NUMA nodes, and memory accesses are interleaved across 2 memory channels.
Auto: Use default value. Current default is NPS1

Default is "Auto".

Package Power Limit

This BIOS switch specifies the maximum power that each CPU package may consume in the system. The actual power limit is the maximum of the Package Power Limit and cTDP.

SMT Control

This BIOS switch allows 2 options: "Auto" and "Disabled". This feature allows enabling or disabling of symmetric multithreading on processors. When enabled, each physical processor core operates as two logical processor cores. When disabled, each physical core operates as only one logical processor core. "Auto" enables this feature and can improve overall performance for applications that benefit from a higher processor core count. Default is "Disabled".

SVM Mode

This BIOS switch allows 2 options: "Enabled" and "Disabled". This is CPU virtualization function. With SVM enabled virtual machines can be installed on the system. Default is "Enabled".