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. Setting 0 disables this feature. It is enabled by default (1).

Firmware / BIOS / Microcode Settings

Operating Modes Selections: (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", allows the user to individually modify any of the low-level settings that are preset and unchangeable in any of the other 4 preset modes.

Platform Controlled Type:

"Maximum Performance" allows the most aggressive use of turbo and power management functions are disabled, thereby increasing power consumption. "Minimal Power" disables turbo and maximizes the use of power management features. 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.

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.

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. 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.

C-States:

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

• 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.
• Disable: When "Disable" 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.

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.

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.

DCA:

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

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.

CPU Frequency Limits:

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. 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.

Energy Efficient Turbo:

When energy efficient turbo is enabled, the CPU's optimal turbo frequency will be tuned dynamically based on CPU utilization.

Uncore Frequency Scaling:

When enabled, the CPU uncore will dynamically change speed based on the workload.

MONITOR/MWAIT:

MONITOR/MWAIT instructions are used to engage C-states.

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

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

XPT prefetch is a mechanism that enables a read request that is being sent to the last level cache to speculatively issue a copy of that read to the memory controller prefetching

UPI Prefetcher

UPI prefetch is a mechanism to get the memory read started early on DDR bus. The UPI receive path will spawn a memory read to the memory controller prefetcher.

Patrol Scrub:

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

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 Enable.

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 A to S may be beneficial in a workload where there are many cross-socket reads.

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:

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

Adjacent Cache Prefetch:

Lightly threaded applications and some benchmarks can benefit from having the adjacent cache line prefetch enabled. Default is enable.

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 enable.

Hardware Prefetcher:

Lightly threaded applications and some benchmarks can benefit from having the hardware prefetcher enabled. Default is enable.

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 enable.

Acoustic Mode

By using acoustic mode, the user has some control over the fan speeds and airflow (and noise) that is produced by the system fans. This mode can be used for noise or airflow concerns in the user environment. As a result, Mode1,2,3,4,5 increase the possibility that the node might have to be throttled to maintain cooling within the fan speed limitation. If there is power or thermal demanding PCI card installed in the chassis, acoustic mode is automatically disabled.

• None: Fan speeds change as required for optimal cooling
• Mode1: Highest acoustics attenuation (lowest cooling)
• Mode2: Higher acoustics attenuation.
• Mode3: Intermediate acoustics attenuation.
• Mode4: Low acoustics attenuation (higher cooling).
• Mode5: Aggressive cooling mode.

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:

[Disable] provides maximum performance but minmum 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 "Syetem Settings" submenu.