SPEC CPU2017 Platform Settings for Lenovo Systems

Operating System Tuning Parameters

sched_cfs_bandwidth_slice_us

This OS setting 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 (ns).

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 8000000 (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 10000000 (ns).

numa_balancing

This OS setting controls automatic NUMA balancing on memory mapping and process placement. NUMA balancing incurs overhead for no benefit on workloads that are already bound to NUMA nodes. Possible settings:

• 0: disables this feature
• 1: enables the feature (this is the default)

For more information see the numa_balancing entry in the Linux sysctl documentation.

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:

• never: entirely disable THP usage.
• madvise: enable THP usage only inside regions marked MADV_HUGEPAGE using madvise(3).
• always: enable THP usage system-wide. This is the default.

THP creation is controlled by the sysfs setting /sys/kernel/mm/transparent_hugepage/defrag. Possible values:

• never: if no THP are available to satisfy a request, do not attempt to make any.
• defer: an allocation requesting THP when none are available get normal pages while requesting THP creation in the background.
• defer+madvise: acts like "always", but only for allocations in regions marked MADV_HUGEPAGE using madvise(3); for all other regions it's like "defer".
• madvise: acts like "always", but only for allocations in regions marked MADV_HUGEPAGE using madvise(3). This is the default.
• always: an allocation requesting THP when none are available will stall until some are made.

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.

cpupower

The OS 'cpupower' utility is used to change CPU power governors settings. Available settings are:

• Performance: Run the CPU at the maximum frequency.
• powersave: Run the CPU at the minimum frequency.
• ondemand: Scales the frequency dynamically according to current load.

tuned-adm

The tuned-adm tool is a commandline interface for switching between different tuning profiles available to the tuned tuning daemon 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:

• throughput-performance: Server profile for typical throughput tuning. This profile disables tuned and ktune power saving features, enables sysctl settings that may improve disk and network IO throughput performance, switches to the deadline scheduler, and sets the CPU governor to performance.
• latency-performance: Server profile for typical latency tuning. This profile disables tuned and ktune power saving features, enables the deadline IO scheduler, and sets the CPU governor to performance.
• enterprise-storage: Server profile to high disk throughput tuning. This profile disables tuned and ktune power saving features, enables the deadline IO scheduler, enables hugepages and disables disk barriers, increases disk readahead values, and sets the CPU governor to performance

dirty_background_ratio

Set through "echo 40 > /proc/sys/vm/dirty_background_ratio". This setting can help Linux disk caching and performance by setting the percentage of system memory that can be filled with dirty pages.

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.

ksm/sleep_millisecs

Set through "echo 200 > /sys/kernel/mm/ksm/sleep_millisecs". This setting controls how many milliseconds the ksmd (KSM daemon) should sleep before the next scan.

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 3> /proc/sys/vm/drop_caches" is used to free pagecache, dentries and inodes.

Firmware / BIOS / Microcode Settings

Power Mode (Default is 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.

• "Saving" 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. "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.
• "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], may be selected after any of the other 4 presets allowing low-level settings, which otherwise are preset and unchangeable, to be individually modified

C1 Enhanced Mode:

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

Sub-NUMA Cluster (SNC):

Sub_NUMA Cluster (SNC) partitions the cores and last level cache (LLC) into clusters with each cluster bound to a set of memory controllers in the system, dividing each CPU package into 2 or 4 NUMA nodes. This can improve average latency to the last level cache and memory. Default is Disabled.

• Disabled:the processor socket is treated as one cluster. No partitioning occurs.
• Enable SNC2 (2-clusters):each socket is divided into two groups, each with its own cores, LLC, and memory controller. System address is divided into two regions, one for each SNC. Required memory configuration to be left/right symmetric.
• Enable SNC4 (4-clusters):each socket is divided into four groups, each with its own cores, LLC, and memory controller. System address is divided into four regions, one for each SNC. Required memory configuration to be fully symmetric (left/right and top/bottom).

Patrol Scrub:

Patrol scrub works in the background to proactively check DIMMs for memory errors. There are two options in this mode: Disabled, Enabled. When "Disabled" is selected, memory latency will be lower but with risk of lower memory reliability. When "Enabled" is selected, memory reliability will be improved. Default is Enabled.

DCU Streamer Prefetcher:

DCU (Level 1 Data Cache) streamer prefetcher is an L1 data cache prefetcher. When the DCU streamer prefetcher detects multiple loads from the same cache line done within a time limit, the DCU streamer prefetcher assumes the next line will be required. The next line is prefetched in to the L1 data cache from memory or L2. Lightly threaded applications and some benchmarks can benefit from having the DCU streamer prefetcher enabled. Default setting is Enabled.

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 setting is Enabled.

Package C State:

The concept of package C-States relates to the state of all the shared resources on the socket, as a function of the individual C-states that the cores enter. Invoking package C-states impacts the state of the mesh and the LLC, the core's power planes and the uncore PLL, and indirectly the state of the integrated peripherals. If set Package C State to special states, when system idle, the core will run at the limited package Cx state. This option allows 6 options: C0/C1 state, C2 state, C6(non Retention) state, C6(Retention) state, No Limit, Auto. Default setting is Auto.

• C0/C1 state:If the "C0/C1 state" is selected in the BIOS, the processor chip always remains active. It can improve the performance of latency sensitive workloads.
• C2 state:Stop the CPU's internal master clock through the hardware, memory path is open.
• C6(non Retention) state:All cores have saved their architectural state and have had their core voltages reduced to zero volts.
• C6(Retention) state:This state provides more power saving than C6 non-retention mode.
• No Limit:C state can downgrade to C10 when system is in idle.
• Auto:C state automatically adjusts based on system load.

LLC Prefetch:

LLC prefetcher is an additional prefetch mechanism on the top of the existing prefetchers that prefetch data into the core DCU amd MLC. Enabling LLC Prefetch gives the core prefetcher the ability to prefetch data directly into the LLC without necessarily filling into the MLC. Default is Disabled.