After upgrading my MacBook Pro to macOS 10.9, I began experiencing issues with consistently high CPU usage.
A detailed examination revealed that the process kernel_task was responsible for generating the excessive load.
After reviewing several discussion forums and Apple Support resources, I discovered that elevated kernel_task activity can sometimes be related to Bluetooth functionality.
Since I use a wireless keyboard and Magic Mouse connected via Bluetooth, disabling Bluetooth permanently was not an option. However, after temporarily turning Bluetooth off for approximately one minute and then re-enabling it, the kernel_task CPU usage dropped back to a normal level of 1–2%.
It appears that the issue may have been caused by a low battery level in my Bluetooth keyboard.