OS Tuning
ulimit:
Used to set user limits of system-wide resources. Provides control over resources available to the shell and processes started by it. Some common ulimit commands may include:
Disabling Linux services:
Certain Linux services may be disabled to minimize tasks that may consume CPU cycles.
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.
Performance Governors (Linux):
In-kernel CPU frequency governors are pre-configured power schemes for the CPU. The CPUfreq governors use P-states to change frequencies and lower power consumption. The dynamic governors can switch between CPU frequencies, based on CPU utilization to allow for power savings while not sacrificing performance.
Other options beside a generic performance governor can be set, such as the Performance governor and Powersave governor:
--governor , -g
The governor defines the power characteristics of the system CPU, which in turn affects CPU performance. Each governor has its own unique behavior, purpose, and suitability in terms of workload.
On many Linux systems one can set the governor for all CPUs through the cpupower utility with following commands:
tuned-adm:
The tuned-adm tool is a commandline interface for switching between different tuning profiles available to the tuned tuning daeomn available in supported Linux distros. The default configuration file is located in /etc/tuned.conf and the supported profiles can be found in /etc/tune-profiles.
Some profiles that may be available by default include: default, desktop-powersave, server-powersave, laptop-ac-powersave, laptop-battery-powersave, spindown-disk, throughput-performance, latency-performance, enterprise-storage
To set a profile, one can issue the command "tuned-adm profile (profile_name)". Here are details about relevant profiles.
Transparent Hugepages (THP)
THP is an abstraction layer that automates most aspects of creating, managing,and using huge pages. It is designed to hide much of the complexity in using huge pages from system administrators and developers. Huge pages increase the memory page size from 4 kilobytes to 2 megabytes. This 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. Most recent Linux OS releases have THP enabled by default.
THP usage is controlled by the sysfs setting /sys/kernel/mm/transparent_hugepage/enabled.
Possible values:
THP creation is controlled by the sysfs setting /sys/kernel/mm/transparent_hugepage/defrag.
Possible values:
An application that "always" requests THP often can benefit from waiting for an allocation until those huge pages can be assembled.
For more information see the Linux transparent hugepage documentation.
Enable LP [Global] (Default = ALL LPs):
Enables Logical processor (Software Method to Enable/Disable Logical Processor threads)
SNC (Sub NUMA) (Default = AUTO):
Disable supports 1-cluster and 4-IMC way interleave. Enable SNC2 supports 2-clusters SNC and 2-way IMC interleave. Enable SNC4 supports 4-cluster and 1-IMC way interleave, Auto - Auto decides based on Si Compatibility.
LLC dead line alloc (Default = Enable):
Enable - opportunistically fill dead lines in LLC. Disable - never fill dead lines in LLC, Auto - Auto decides based on Si Compatibility.
Patrol Scrub (Default = Enable at End of POST):
This option allows for correction of soft memory errors. Over the length of system runtime, the risk of producing multi-bit and uncorrected errors is reduced with this option. Values for this BIOS setting can be:
Xtended Prediciton Table (XPT) Prefetch (Default = Auto):
This option configures the processor Xtended Prediciton Table (XPT) prefetch feature. The XPT prefetcher exists on top of other prefetchers that that can prefetch data in the core DCU, MLC, and LLC. The XPT prefetcher will issue a speculative DRAM read request in parallel to an LLC lookup. This prefetch bypasses the LLC, saving latency. In some cases, setting this option to disabled can improve performance. In some cases, setting this option to disabled can improve performance. Typically, setting this option to enable provides better performance. This option must be enabled when Sub-NUMA Clustering is enabled. Values for this BIOS option can be:
DCU Streamer Prefetcher (Default = Enable):
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 Bias (Default = Balanced Performance):
Use input from ENERGY_PERF_BIAS_CONFIG mode selection. PERF/Balanced Perf/Balanced Power/Power
Intel VT for Directed I/O (Default = Enable):
Enable/Disable Intel Virtualization Technology for Directed I/O (VT-d) by reporting the I/O device assignment to VMM through DMAR ACPI Tables.
Hardware P-States (Default = Native Mode):
Disable: Hardware chooses a P-state based on OS Request (Legacy P-States) Native Mode:Hardware chooses a P-state based on OS guidance Out of Band Mode:Hardware autonomously chooses a P-state (no OS guidance)
Last updated March 18, 2021.