Hello to all,
Some months ago, I posted the solution that was working for me: vacuum-cleaning the fans of my MacBook Pro. I believed that this resulted in breaking the vicious circle of overheating and kernel_task running amok. I was repeating this procedure each time the computer seemed to slow down, every couple of months or so. Last time, however, a bit over a month ago, the effect lasted only very shortly. But while the kernel_task still was putting an exagerate load on the CPU, two and only two specific applications–always running on this machine–were taking their toll: Firefox (up to 150% CPU usage, regardless of version) and iTunes (constantly varying between 50 and 110% or so). I have posted elsewhere how I had also managed to reduce iTunes' CPU usage by tackling its (unrequested) desires to access the iTunes Store, but this didn't seem to have an effect any longer.
I was therefore going to look into the workarounds posted here lately, in particular the detailed one offered by rdoxenham.com. However, the machine had to be sent in for repair before that, as something rather curious had happened.
I basically never use this MBP's battery: it's always on its desk, plugged in to the Cinema Display's power supply. This is probably the reason I didn't notice anything wrong until the battery was drained within a few minutes during a power failure. I then found this warning in the Energy Saver pref. panel: "Service battery. Estimated time until full: ", where I can't remember the value I saw after "full:" the first time I looked. But within a few days it had turned into this: "Estimated time until full: (null) 0%". Simultaneously, the values returned by SystemProfiler for the battery were looking pretty erratic compared to another, well-functioning MacBook Pro I have here. Moreover: by the time I'd got things sorted out to drop the MBP at the Apple retailer who then would forward it under Applecare to Apple's regional workshop (the whole procedure took over a week), the battery wasn't showing anywhere anymore, in any application or utility. The person at the Apple retailer said he'd never seen such a thing in his years selling and servicing Macs.
Why all this on this thread right now? The battery was duly replaced. When I did ask them later, I was informed that the only thing performed by the tech together with the battery replacement had been a ritual SMC reset, which I believe I also did when I was originally trying to get to terms with the slowdowns. But the main point is that since getting the MBP back–that was two weeks ago–the slowdowns are completely gone and the activity monitor is showing absolutely reasonable one-digit CPU uses, with an occasional, very brief peak up to 30-40% if, for example, Firefox is loading a Flash video.
I'm not competent to determine the exact interactions between the battery turning bad, the kernel_task or other applications running wild, the computer overheating, and even the SMC reset. Which of these causes the others is beyond my understanding. But at this point I'd strongly suggest to anyone with this particular issue to take a look at the condition of their battery.