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

SNC:

SNC (Processor Sub-NUMA Clustering) partitions Intel Xeon Scalable processor cores and last-level cache (LLC) into disjoint clusters with each cluster bound to a set of memory controllers in the system. There are two options in this mode: Disable, Enable SNC2 (2-clusters). Default is Disable.

• "Disable" When "Disable" is selected, the LLC is treated as one cluster.
• "Enable SNC2 (2-clusters)" When "Enable SNC2" is selected, it will create 2-way Sub-NUMA Clusters for each Xeon Scalable Family and next generation of Xeon Family CPU. Utilizes LLC capacity more efficiently and reduces latency due to core/Integrated Memory Controller proximity.

Patrol Scrub:

Patrol scrub works in the background to proactively check DIMMs for memory errors. There are two options in this mode: Disable, Enable. Default is Enable.

• "Disable" When "Disable" is selected, memory latency will be lower but with risk of lower memory reliability.
• "Enable" When "Enable" is selected, memory reliability will be improved.

Power Performance Tuning:

Allows the OS or BIOS or PECI to control the Energy Performance Bias. Default setting is OS controls EPB.

ENERGY_PERF_BIAS_CFG mode:

This BIOS option allows for processor performance and power optimization. There are four options in this mode: Performance, Balanced Performance, Balanced Power, Power. Default is Balanced Performance.

• "Performance" High performance with less need for power saving.
• "Balanced Performance" Provides optimal performance efficiency.
• "Balanced Power" Provides optimal power efficiency.
• "Power" High power saving with less need for performance.

CPU C6 report:

Allows the BIOS to report the CPU C6 State (ACPI C3) to the operating system. During the CPU C6 State, the power to all cache is turned off. There are two options in this mode: Disable, Enable. Default is Enable.

XPT Prefetcher:

XPT prefetcher 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. Default setting is Disable.

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.

Adjacent Cache Prefetch:

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

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 setting is Enable.