Summary

Dell PowerEdge servers provide a wide range of tunable parameters to allow customers to achieve top performance. The information in this paper outlines the tunable parameters available in the latest generation of PowerEdge servers (for example, R660, R760, MX760, and C6620) and provides recommended settings for different workloads.

Figure 1. PowerEdge R660

Figure 2. PowerEdge R760

The following tables provide the BIOS setting recommendations for the latest generation of PowerEdge servers.

 Table 1. BIOS setting recommendations—System profile settings

[1] Depends on how system was ordered. Other System Profile defaults are driven by this choice and may be different than the examples listed. Select Performance Profile first, and then select Custom to load optimal profile defaults for further modification

[2]  SST Turbo Boost Technology is substantially better than previous generations for latency-sensitive environments, but specific Turbo residency cannot be guaranteed under all workload conditions. Evaluate Turbo Boost Technology in your own environment to choose which setting is most appropriate for your workload, and consider the Dell Controlled Turbo option in parallel.

[3]  Monitor/Mwait should only be disabled in parallel with disabling Logical Processor. This will prevent the Linux intel_idle driver from enforcing C-states.

[4]  You can test your own environment to determine whether disabling Memory Patrol Scrub is helpful.

[5]  Dynamic selection can provide more TDP headroom at the expense of dynamic uncore frequency. Optimal setting is workload dependent.

[6]  Autonomous on Air Cooled system or Disabled on Liquid Cooled Systems

Table 2. BIOS setting recommendations—Memory, processor, and iDRAC settings

[1] Use Optimizer Mode when Memory Bandwidth Sensitive, up to 33% BW reduction with Fault Resilient Mode.

[2] Only available when x4 DIMMS installed in the system.

[3]  Logical Processor (Hyper Threading) tends to benefit throughput-oriented workloads such as SPEC CPU2017 INT and FP_RATE. Many HPC workloads disable this option. This only benefits SPEC FP_rate if the thread count scales to the total logical processor count.

[4]  Dell Controlled Turbo helps to keep core frequency at the maximum all-cores Turbo frequency, which reduces jitter. Disable if Turbo disabled.

[5]  Option is available on liquid cooled systems only.

[6]  Depends on if your program is affected by Base and Turbo frequency. Will reduce CPU core count and give higher Base and Turbo frequencies.

iDRAC recommendations

• Thermally challenged environments should increase fan speed through iDRAC Thermal section.
• All Power Capping should be removed in performance-sensitive environments.

BIOS settings glossary

• System Profile: (Default=Performance Per Watt)—It can be difficult to set each individual power/performance feature for a 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.
• Performance Per Watt DAPC (Dell Advanced Power Control)—This mode uses Dell presets to maximize 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.
• Performance Per Watt OS—This 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 "Performance Per Watt DAPC" mode. In this mode, no bus speeds are derated as they are in the Performance Per Watt DAPC mode, leaving the operating system in control of those changes.
• Performance—This mode maximizes the absolute performance of the system without regard for power. In this mode, power consumption is not considered. Things like fan speed and heat output of the system, in addition to power consumption, might increase. Efficiency of the system might go down in this mode, but the absolute performance might increase depending on the workload that is running.
• Custom—Custom mode allows the user to individually modify any of the low-level settings that are preset and unchangeable in any of the other four preset modes.
• C-States—C-states reduce CPU idle power. There are three options in this mode:
  • Enabled: When “Enabled” is selected, the operating system initiates the C-state transitions. Some operating system software might defeat the ACPI mapping (for example, intel_idle driver).
  • Autonomous: When "Autonomous" is selected, HALT and C1 requests get converted to C6 requests in hardware.
  • Disable: When "Disable" is selected, only C0 and C1 are used by the operating system. C1 gets enabled automatically when an OS auto-halts.
• 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 period of time when it is in turbo mode.
• Hyper-Threading—Enabling Hyper-Threading lets the operating system address 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.
• Execute Disable Bit—The execute disable bit allows memory to be marked as executable or non-executable when used with a supporting operating system. This can improve system security by configuring the processor to raise an error to the operating system when code attempts to run in non-executable memory.
• 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.
• Per Core P-state—When per-core P-states are enabled, each physical CPU core can operate at separate frequencies. If disabled, all cores in a package will operate at the highest resolved frequency of all active threads.
• CPU Frequency Limits—The maximum turbo frequency can be restricted with turbo limiting to a frequency that is between the maximum turbo frequency and the rated frequency for the CPU installed.
• 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: Uses LLC capacity more efficiently and reduces latency due to core/IMC proximity. This might provide performance improvement on NUMA-aware operating systems.
• Snoop Preference—Select the appropriate snoop mode based on the workload. There are two snoop modes:
  • HS w. Directory + OSB + HitME cache: Best overall for most workloads (default setting)
  • Home Snoop: Best for BW sensitive 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 prefetcher.
• 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 that runs a background memory scrub against all DIMMs. This feature can negatively affect 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 Enabled.
• LLC Dead Line Allocation—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 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 systems. Default is Enabled.
• Hardware Prefetcher—Lightly threaded applications and some benchmarks can benefit from having the hardware prefetcher enabled. Default is Enabled.
• Trusted Execution Technology—Enable Intel Trusted Execution Technology (Intel TXT). Default is Disabled.