By Nishanth Dandapanthula and Garima Kochhar
HPC (High Performance Computing) mode is a new feature introduced in the BIOS which improves the performance of certain workloads on Dell servers based on AMD Interlagos processors. This blog describes how to enable and take advantage of the HPC mode and includes some performance results of the impact of HPC mode on a PowerEdge R815 server.
Enabling HPC mode through BIOS
The BIOS version which introduces HPC mode on the R815 is 2.8.2. To enable HPC mode through the BIOS, the BIOS must be set as shown in Table 1. Figure 1 and 2 show the screenshots of the steps involved in enabling HPC mode through the BIOS. Note that setting the HPC mode to “enabled” within the Processor Settings tab alone will not fully enable HPC mode.
Table 1: Enabling HPC mode through BIOS
Figure 1: Enable HPC mode in the Processor Settings tab
Figure 2: Change options in the Power Management Tab
Enabling HPC mode through DTK
To enable HPC mode in a cluster environment, Dell’s OpenManage Deployment Toolkit can be used. The power management settings which are listed above can be set using the existing syscfg command line. The new parameter for HPC mode is “--hpcmode”. This parameter is being introduced with DTK v4.1.Details are listed in Table 2 below.
Table 2: HPC mode through DTK
The Red Hat Enterprise Linux kernel 2.6.32-220.17.1.el6 or later is needed for HPC mode to function. Without the support enabled in this kernel, the server will kernel panic on boot when HPC mode in enabled in the BIOS.
Impact of HPC mode
To measure the impact of HPC mode on the performance of the server we used the High Performance Linpack (HPL) benchmark. The prebuilt HPL binaries were obtained from http://developer.amd.com/libraries/acml/downloads/pages/default.aspx. These binaries were built using Open64 compilers. Table 3 shows the test server configuration and Table 4 details the performance results. This evaluation was done on a single server.
Table 3: Test Server Configuration
Table 4: Impact of HPC mode
From Table 4, it can be seen that HPC mode provides up to 6% improvement in HPL efficiency. This increased performance is at the expense of higher power consumption and is recommended only for those environments where the power available can support this mode of operation. Another caveat to be noted is that the performance improvement provided by HPC mode for workloads other than HPL is minimal.
The table compares the results of the new “HPC mode” BIOS option to the previous “Max Performance” Power Management option. For the “HPC mode” BIOS option to take effect, it is mandatory that the “Power Management” option must be set to “Custom”, the “CPU Power and Performance Management” option must be set to “OS DBPM” and the “Fan Power and Performance Management” option must be set to “Maximum Performance”.