Written by Topher Kessler
There have been many reports, especially with MacBook Air and other laptop owners, where the Mac OS X "kernel_task" process takes up a large amount of CPU when checked in Activity Monitor. When this happens, the computer may run slower and also may appear to be running hot as well.
The kernel_task is a software process that lumps together many of the current "tasks" that the kernel is performing. In OS X, the kernel is a software architecture that is responsible for handling resources that other processes need, such as preemptive multitasking, virtual memory, process communication, some scheduling, and console input. In addition, the BSD subsystem in OS X is also tightly integrated into the kernel, which brings technologies such as networking and file system management down to the kernel level.
The kernel also can be modified and given enhanced functionality in real time, which is generally seen in the form of kernel extensions that can be dynamically loaded through the I/O kit, giving the system plug-and-play functionality.
All of these features of the kernel mean that there are a variety of possibilities why the kernel_task process could be running, and as such there are many small things that can be tried to pinpoint a problem. Keep in mind that while the kernel_task may be what appears to be using up CPU processes, it is some underlying function that is using up the CPU and just being reported through kernel_task. These functions can be anything, such as a hardware device that is trying to communicate with another device, and not necessarily a software process.
Given the number of functions lumped into "kernel_task", there are several things you can try to go about pinpointing the cause of CPU usage by the kernel:
Remove external devices you may have attached to your system. These can include hard drives, audio interfaces, scanners and printers, cameras, and input devices.
Shut down all system hardware enhancements such as Wi-Fi, Bluetooth, and the infrared receiver. Additionally, switch GPUs for computers with multiple graphics processors (MacBooks with Geforce 9400M chipsets).
Boot into Safe Mode, which will load only the basic kernel extensions, and help you pinpoint whether the problem is with third-party kernel extensions.
Disable software enhancements. These include the firewall by setting it to allow all incoming connections, setting network interfaces to be inactive (using the gear menu in the "Network" system preferences), turning off sharing services such as file and web sharing, and toggling the use of secure virtual memory in the "Security" system preferences.
Reset PRAM and SMC. While this has not been too successful in most cases, firmware settings could contribute to kernel activity.
Change system preference settings by methodically going through each system preference setting and changing it, by either disabling and re-enabling it, or slightly adjusting its value (the sleep timer sliders). This can help refresh any faulty settings that could be causing problems.
Check for system processes other than "kernel_task" that may be using up CPU as well. If they are, then they could be calling for the kernel to use up more resources. Check our guide on OS X system processes to see which ones can be safely shut down through Activity Monitor.
Reduce system heat. The physical environment of the computer can contribute to the kernel trying to compensate for increased heat. If your computer's vents are obstructed then the kernel may ramp up in trying to prevent overheating. You can try changing the CPU speed to the "reduced" setting in the Energy Saver system preferences, and also consider moving your system to a cooler place (a tabletop instead of a bed or your lap, for portables).
Perform these suggestions with Activity Monitor open, and if any of them result in lower CPU usage by kernel_task, then you can further troubleshoot the respective setting.
Topher has been an avid Mac user for the past 10-15 years, and has been a contributing author to MacFixIt for just over a year now. One of his diehard passions has been troubleshooting Mac problems and making the best use of Macs and Apple hardware both for family and friends, as well as in the workplace. He and the newly formed MacFixIt team are hoping to bring enhanced and more personable content to our readers, and keep the MacFixIt community going here at CNET. If you have questions or comments for Topher or the other MacFixIt editors, feel free to contact us at http://www.macfixit.com/contactResources