Friday, January 3, 2014

CentOS/RHEL : Change CPU Frequency

Few days ago I was asked by someone in our organization to set the CPU frequency to maximum on one of our red hat 6.2 servers

The first thing to do here was to check the reason for this unusual request. Do not immediately attempt to change the CPU frequency without understanding the implication of such changes.

The second thing to do, was to check the current cpu frequency. This can achieved by either:

1. Installing nice set of tools called cpupowerutils:

yum install cpupowerutils

Next, check the frequency with cpufreq-info:

[root@mario~]# cpufreq-info
analyzing CPU 0:
driver: acpi-cpufreq
CPUs which need to switch frequency at the same time: 0
hardware limits: 1.33 - 2.00 GHz
available frequency steps: 1.33 GHz, 1.60 GHz, 2.00 GHz
available cpufreq governors: userspace, ondemand, conservative, powersave, performance
current policy: frequency should be within 1.33 MHz and 2.00 GHz.
                The governor "conservative" may decide which speed to use
                within this range.
current CPU frequency is 1.33MHz.

2. Without cpupowerutils, you can look at sysfs

ls /sys/devices/system/cpu/cpu[cpu number]/cpufreq/

You will find there the max, min and current cpufrequency  with other bunch of useful files

Now, to change to cpu frequency to maximum can by done also by either:

1. Using cpupowerutils

cpupower frequency-set -g performance 

2. setting the the wanted value in sysfs

echo 1300000 > /sys/devices/system/cpu/cpu[cpu number]/cpufreq/scaling_min_freq

This will not allow the CPU getting below the specified value

### Be sure you understand what you are trying to achieve ###

You can find the full documentation HERE


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