Intel CPU Frequency Tuning for (Flex) RAN Workloads managed by Telco Cloud Platform (TCP) RAN

Products

• VMware Telco Cloud Automation
• VMware Telco Cloud Platform RAN

Issue/Introduction

While running FlexRAN workloads on SapphireRapid CPUs on ESXi 8.0U2, Broadcom's current recommendation is to directly set the CPU frequencies to the vendor recommended value for a given processor family type. The tuning of the CPU frequencies is done by setting a Model Specific Register (MSR) 774.

For example, on a processor family where the vendor recommended CPU frequency is 2.5GHz, which translates to 0x19 in hexadecimal. To control the frequency, the Minimum Performance, Maximum Performance, and Desired Performance should be all be set to the same 2.5 GHz value.

Resolution

To write the the Model Specific Register 774 and keep the settings persistent across ESXi host reboot, append the following to the init script at /etc/rc.local.d/local.sh in the ESXi host:

#Set the FREQ value to the proper frequency for your CPU model.
#Example: Changing 2.5 GHz -> 25 -> 0x19 -> 0x80001919
FREQ=0x80001919
for cpu in `vsish -e ls /hardware/cpu/cpuList`
do
   vsish -e set /hardware/msr/pcpu/${cpu}/addr/0x774 ${FREQ}
done
 

NOTE: The 2.5 GHz value of FREQ used here is just an example. The value varies for each processor type. Please make sure to use the correct value for your processor model.

To verify the Frequency is set you can use the following command:

vsish -e get /hardware/msr/pcpu/0/addr/0x774

Note: (0 is for cpu 0, can check them all by changing this number.)