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.

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

Choose Operating Mode: (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 Mode", may be selected after any of the other 4 presets allowing low-level settings, which otherwise are preset and unchangeable, to be individually modified

Page Policy:

Adaptive Open Page Policy can improve performance for applications with a highly localized memory access pattern; Closed Page Policy can benifit applications that access memory more randomly. Default is Adaptive.

CPU P-state Control:

Select the method used to control CPU P-states (performance states). "None" disables all P-states and the CPUs run at either their rated frequency or in turbo mode (if turbo is enabled). When "Legacy" is selected, the CPU P-states will be presented to the operating system (OS) and the OS power management (OSPM) will directly control which P-state is selected. With "Autonomous", the P-states are controlled fully by system hardware. No P-state support is required in the OS or VM. "Cooperative" is a combination of Legacy and Autonomous. The P-states are still controlled in hardware but the OS can provide hints to the hardware for P-state limits and the desired setting. With "Cooperative without Legacy", uses Intel native hardware p-states without Legacy p-state control (No OS controlled p-states). Starts with Autonomous mode until the OS swtiches to Cooperative. With "Cooperative with Legacy", uses Intel native hardware p-states but Legacy p-state control. Starts with Legacy p-states until the OS swtiches to Cooperative. When a preset mode is selected, the low-level settings are not changeable and will be grayed out. If user would like to change the settings, please choose "Custom Mode" in "Operating Mode" located under "System Setting" submenu. Default is Autonomous.

C-States:

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

• 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.
• Disabled: When "Disabled" 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. Default is Enabled.

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. When a preset mode is selected, the low-level settings are not changeable and will grayed out. If user would like to change the settings, please choose [Custom Mode] in "Operating Mode" located under "System Settings" submenu. Default is Enabled.

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. Default is Enabled.

DCA:

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

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. Default is Platform Controlled.

CPU Frequency Limits:

When the CPU Frequency Limit parameter is set to the Restrict Maximum Frequency setting, the maximum frequency (turbo, AVX, and non turbo) can be restricted to a frequency that is between the maximum turbo frequency for the CPU installed and 1.2GHz in 100MHz increments. This can be useful for synchronizing CPU task. Note, the max frequency for N+1 cores cannot be higher than N cores. If an illegal frequency is entered, it will automatically be limited to a legal value. If the CPU frequency limits are being controlled through application software, leave this menu item at the default ([Full turbo uplift]), please choose [Custom Mode] in "Operating Mode" and [Enable] in "Turbo Mode" located under "System Setting" submenu. Default is Full turbo uplift.

Uncore Frequency Scaling:

When enabled, the CPU uncore will dynamically change speed based on the workload. All miscellaneous logic inside the CPU package is considered the uncore. Default is Enabled.

MONITOR/MWAIT:

MONITOR/MWAIT instructions are used to engage C-states. MONITOR/MWAIT OS instructions are used to enable/disable c-states. If a user disables c-states in UEFI and wants to prevent the OS from overriding that setting, the user should set MONITOR/MWAIT=Disabled. Default is Enabled.

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

Default is Disabled.

Snoop Preference:

Select the appropriate snoop mode based on the workload. There are two snoop modes: "Home Snoop Plus" and "Home Snoop". Default is "Home Snoop Plus".

• Home Snoop Plus: Best overall for most workloads.
• Home Snoop: Best for BW sensive workloads.

XPT Prefetcher

When enabled, enables a read request that is sent to the processor last level cache to speculatively issue a copy of that read request to the processor memory controller prefetcher to reduce latency. The performance benefit can vary so the end user must determine whether or not enabling the XPT prefetcher benefits their specific application environment. Default is Enabled.

UPI Prefetcher

When enabled, memory reads on the memory bus can be started earlier by the processor memory controller to reduce latency. The performance benefit can vary so the end user must determine whether or not enabling the UPI prefetcher benefits their specific application environment. Default is Enabled.

Patrol Scrub:

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

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 Enabled.

Stale AtoS

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:

• Disable: Disabling this option allows the feature to process memory directory states as described above.
• Enable: 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 AtoS may be beneficial in a workload where there are many cross-socket reads. Default is Auto.

LLC dead line alloc

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:

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

Default is Enable.

Adjacent Cache Prefetch:

When enabled, fetches both cache lines that make up a 128 byte cache line pair even if the requested data is only in the first cache line. Lightly threaded applications and some benchmarks can benefit from having the adjcent cache line prefetch enabled. Default 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 is Enabled.

Hardware Prefetcher:

When enabled, fetches the next cache line into the processor L2 cache if two consecutive cache lines were read. The next cache line is fetched from memory. Lightly threaded applications can benefit from having the hardware prefetcher enabled. But, the end user must determine whether or not enabling the hardware prefetcher benefits their specific application environment. Default is Enabled.

DCU IP Prefetcher:

DCU IP Prefetcher is typically best left enabled for most environments. Some environments may benefit from having it disabled(e.g. Java). Default is Enabled.

Workload Configuration:

I/O sensitive should be used with expansion cards that require high I/O bandwidth when the CPU cores are idle to allow enough frequency for the workload. Default is Balanced.

Memory Power Management:

Allows the platform to put the memory into a lower power consumption state. Performance may be reduced. [Disabled] provides maximum performance but minimum power savings. [Automatic] is suitable for most applications. When a preset mode is selected, the low-level settings are not changeable and will grayed out. If user would like to change the settings, please choose [Custom Mode] in "Operating Mode" located under "System Settings" submenu. Default is Disabled.

Memory Data Scrambling:

Uses a data scrambling feature in the memory controller to create pseudo-random patterns on the DDR4 data bus to reduce possibility of data-bit errors due to the impact of excessive current fluctuations. Default is Enabled.

UPI Link Disable:

Disabling one of the CPU UPI links can save power. If maximum performance is desired, all UPI links should be left enabled. When a preset mode is selected, the low-level settings are not changeable and will be grayed out. If user would like to change the settings, please choose [Custom Mode] in "Operating Mode" located under "System Setting" submenu. Note, for some highly NUMA optimized workoads, maximum performance may be achieved by setting 'Disabled 1 Link'. Default is Enabled ALL Links.

LLC Prefetch:

The LLC prefetcher is a new prefetcher added to the Intel Xeon Scalable family as a result of the non-inclusive cache architecture. Enabling LLC Prefetch gives the core prefetcher the ability to prefetch data directly into the LLC without necessarily filling into the MLC. Default is Disable.