Dell PowerEdge 1655MC - Manual (Page 11)

Optimal BIOS settings for HPC with Dell PowerEdge 12 th generation servers
11
CPU Power Management determines what controls the power management for the processor.
System DBPM (Demand Based Power Management) is Dell’s Active Power Controller (DAPC) and is
hardware-based control from the iDRAC. OS DBPM hands control to the Operating System. In the
case of Linux, this is controlled by the “cpuspeed” service. Maximum Performance maintains full
voltage to internal components, such as memory and fans, even during periods of inactivity, thus
eliminating the performance penalty associated with phase transitions. This is suitable for
customers whose aim is to extract the highest performance from a server, potentially at the
expense of higher power consumption.
Memory Frequency sets the speed at which the memory will operate. This depends on the actual
DIMMs used and the memory configuration of the system. The Max Performance System Profile will
set the memory speed to run at the maximum supported by the configuration. With BIOS v1.1.2 and
later, Max Reliability picks the speed that is one less than Max Frequency. With the Custom System
Profile, any supported memory speed can be explicitly set. Note that the Memory Frequency does
have a dependency on the operating Memory Voltage. For example 1.35V DIMMs cannot run at
1600MT/s at the time of writing.
Turbo Boost enables or disables the Turbo feature of the Intel Xeon E5-2600 processors. This
option is described in Section 3.2.
The C States and C1E options are used to enable or disable these features. These are power saving
features that allow frequency scaling to individual CPU cores, as opposed to DBPM that functions at
the socket level. This technology is similar to that introduced with Dell’s previous generation
servers
The Memory Patrol Scrub setting determines how often the system memory is checked. Patrol
Scrub searches the memory for errors and repairs correctable errors. This feature prevents
accumulation of errors. The Standard setting specifies that patrol scrubbing will occur at the
standard or default rate of once every 24 hours. Extended sets the scrub to occur every hour.
Disabled turns this feature off.
Memory Refresh Rate This setting determines how often the memory is refreshed. The 2x option
allows the memory to operate more reliably by refreshing the memory data at twice the normal
rate, at the expense of performance.
Monitor/Mwait is a new BIOS option. When this option is disabled, it prevents the OS from using the
MWAIT instructions on the CPU. Use of these instructions can cause C3, C6 or C7 states to be
engaged depending on the silicon. The intel_idle driver in certain newer operating systems can
engage C-states even when C States and C1E are explicitly disabled. Disabling the Monitor/Mwait
setting makes sure that none of these lower sleep states are engaged and the CPU remains fully
turned on. This setting should be disabled only when C States and Logical Processor options are also
set to disabled. An alternative to the BIOS setting is to disable the intel_idle driver in the operating
system. For example, with Red Hat Enterprise Linux 6.2 the kernel string
“intel_idle.max_cstate=0” can be used to disable intel_idle.
Looking back at Table 3, it is now easier to understand what each of the canned System Profiles is
trying to accomplish. The Performance Per Watt Optimized options balance system performance
with energy efficiency. Turbo Boost is enabled, but so are C States and C1E to conserve power. The
Memory options are set to their basic settings. The choice here is between the system-based power
management, DAPC, or OS-based.