CPU Frequency - sysfs - core

What it does #

This metric provider reads the current CPU frequency from the Linux sysfs subsystem for every core. It does this throug a simple bash script just cat-ting the file endpoint.

Classname #

• CpuFrequencySysfsCoreProvider

Metric Name #

• cpu_frequency_sysfs_core

Input Parameters #

• args
  • -i: interval in milliseconds

By default the measurement interval is 100 ms.

./get-scaling-cur-freq.sh -i 100

Output #

This metric provider prints to Stdout a continuous stream of data. The format of the data is as follows:

TIMESTAMP READING CORE

Where:

• TIMESTAMP: Unix timestamp, in microseconds
• READING: The current frequency of the core in Hz
• CORE: The core ID assigned by the Linux sysfs

Any errors are printed to Stderr.

How it works #

Linux offers the current frequency of the cores as a read-out of a processor internal register to the user-space in the sysfs. We just read this file endpoint periodically.

Caveats #

If you have very many cores you will generate a lot of data which is tricky to interpret as Linux constantly swaps cores and measurements are not directly comparable core-to-core to each other.

For most user the detail output of this provider will rather be noise than valuable data.

We recommend to either only look at the aggregate data to understand how the cores behave individually or only turn the provider on if you want to debug the behaviour of your measurement.

Troubleshooting #

The provider cannot be used if you do not have read access to /sys and more specifically /sys/devices/system/cpu/.

Especially on VMs this directory often does not exist.