After installing the latest OSX combo update. My computer able to boot normally, but once the desktop loaded, the fan speed going up and stay at around 1300rpm rather then going down. And then I realise that "kernel_task" always use about 20% CPU in my single CPU Mac Pro 4,1 (flashed 5,1). The CPU A current in the istat manual shows a minimum 50A (voltage stay at 1.2V) even though no other loading to the CPU. I suspect this abnormally high current cause the extra heat. Since my fan control setting basically directly related to the heatsink temperature. More heat means more noise.
I did a SMC and PRAM reset, but nil help.
One of the suggestion from google search is to remove the MacPro5_1.plist file in ACPI_SMC_PlatformPlugin.kext.
After I remove that file and reboot, the problem seems fixed. However, when I run GeekBench, the score is just a bit more than 7000 (it should be around 16000). No matter how hard I push the CPU (e.g. running Handbrake), the CPU A current only shows around 20A. Even though the CPU usage is above 1100% for my W3690. The CPU heatsink temperature stay at 40C, intake/exhaust fan ran at 800rpm, but only able to deliver half of its performance (in all benchmark software and handbrake).
Since the ACPI_SMC_PlatformPlugin.kext is SMC related, and my Mac Pro 4,1 is actually using the 4,1 SMC but 5,1 firmware. I decided to rename the MacPro4_1.plist to MacPro5_1.plist.
After this little modification. The system now completely normal. The CPU voltage will vary between 0.9V-1.3V, the current will vary between 5A - 80A. No more kernel_task abnormal high CPU usage.
If anyone has this issue after any OS update. May be this is the solution for you.
Or if anyone want to force your Mac Pro running in a very low power but cool mode. May be you can try to remove that MacPro5_1.plist file
I did a SMC and PRAM reset, but nil help.
One of the suggestion from google search is to remove the MacPro5_1.plist file in ACPI_SMC_PlatformPlugin.kext.
After I remove that file and reboot, the problem seems fixed. However, when I run GeekBench, the score is just a bit more than 7000 (it should be around 16000). No matter how hard I push the CPU (e.g. running Handbrake), the CPU A current only shows around 20A. Even though the CPU usage is above 1100% for my W3690. The CPU heatsink temperature stay at 40C, intake/exhaust fan ran at 800rpm, but only able to deliver half of its performance (in all benchmark software and handbrake).
Since the ACPI_SMC_PlatformPlugin.kext is SMC related, and my Mac Pro 4,1 is actually using the 4,1 SMC but 5,1 firmware. I decided to rename the MacPro4_1.plist to MacPro5_1.plist.
After this little modification. The system now completely normal. The CPU voltage will vary between 0.9V-1.3V, the current will vary between 5A - 80A. No more kernel_task abnormal high CPU usage.
If anyone has this issue after any OS update. May be this is the solution for you.
Or if anyone want to force your Mac Pro running in a very low power but cool mode. May be you can try to remove that MacPro5_1.plist file
Last edited: