slow MBP 15-inch Late 2011: kernel_task and cpu speed limited to 0.8 GHz

hopefullost

macrumors newbie
Original poster
Mar 27, 2019
2
0
Machine is a friend's. He reported extreme slowness under light load.

MacBook Pro 15 inch, late 2011
- 2.4Gz i7
- 8GB RAM
- 5400 rpm hdd with tons of free space, not encrypted
(a fairly recent replacement, done at the Apple Store 1-2 years back, he says)
- macOS Sierra 10.12.6
- normal battery and 85W charger

The initial symptom with this machine was kernel_task consuming CPU. This started inconsistently, but as soon as 5 minutes after boot, with as little as one Safari tab open. TG Pro shows all temp sensors reporting 30-60C temps and fans running slowly at 2k rpm or less throughout.

The CPU speed also seems capped at 800 MHz from boot, except in safe mode. I am looking at this with `pmset -g therm` and Intel Power Gadget, and I've run a few Geekbench CPU tests with uniformly horrible results.

Neither kernel_task nor CPU speed cap appears in safe mode. Removing the machine's plist for ACPI_SMC_PlatformPlugin kext eliminates the kernel_task symptom. So I can bandaid that away, if I think it's safe. Possibly I can configure TG Pro to intervene if it sees the machine actually getting hot, too. But the CPU speed still bugs me.

I've tried:
- safe mode boot: neither kernel_task nor CPU speed issue appears.
- look for and remove startup items, agents, daemons
- SMC reset
- NVRAM/PRAM reset
- creating and logging in as a new user
- hardware test, normal and extended (no problems found)
- geekbench CPU tests
(Seeing if CPU speed steps up, temps rise, or kernel_task recurs under load. None of the above. Geekbench numbers are awful compared to similar machines. sample result: https://browser.geekbench.com/v4/cpu/12545248)
- disk utility 'first aid'
- reinstall Sierra from recovery (without erasing disk)
- open case and blow out dust: no dust; very clean.

I have not tried:
- booting from another disk, another OS, or doing a full disk erase and clean reinstall.
- looking inside for hardware issues or signs of damage.
- taking to the Apple Store

Any suggestions?
I'm about ready to apply the ACPI_SMC_PlatformPlugin bandaid and tell my friend that it's usable for light work but if he wants to get the full performance out of it he can try taking it to the Apple Store.

I don't have much experience with the Apple Store. Are they likely to be able to help him much with this?
 

Audit13

macrumors 601
Apr 19, 2017
4,406
1,111
Toronto, Ontario, Canada
The MacBook could be suffering from the a failing GPU for which the 2011 15" MBPs are famous for.

The limited cpu speed could be due to a bad battery. Try disconnecting the battery and booting the machine.

The sata hard drive cable could also be failing.

The MacBook is considered a vintage or legacy model so the Apple store may or may not run diagnostics. Even if they did run diagnostics, it may actually pass.

I would not spend or spend very little to get it working.