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This is the comment you were replying to, attached to the article Getting my computer back - or - where's the processing power?:

#7 No silver bullet! Posted by k8to (64.142.xx.xx) on Sun 1 Jan 2006 at 21:29 You can't just provide a simple series of steps to find out where the performance has gone. This is a problem analysis situation where you just have to investigate and find the problem or problems. The recommendations of top, filelight, etc. are good, but these are all step 2 type actions. The first action is to accurately determine what kind of a problem you are having. Is it really CPU starvation you are not happy about? Is it visual responsiveness in your gui? Is it program launch time? Recognizing what "seems slow" and verifying that your guess is right is step 1. For example, at one point in my last six months or so in using Debian, the interface became "slow". I tried some normal cpu-intensive tasks, and they ran about as I would expect, so it wasn't that my computer had started failing or cache had been disabled, or the CPU was being hogged or anything. Then I tried launching some large programs (like the huge pig azureus), and this was the same as it had been previously. Then I started thinking the problem was in the gui layer, and tried quickly swapping from workpace to workspace, and this was very much slower than usual. Armed with the information that the slowdown was in the gui, I looked at my X server, which wasn't swapping. I experimented with some window movement and creation stuff, and decided that somehow in the move from XFree to XOrg I had lost a great deal of X buffer performance. Bad drivers? AGPgart disabled? After a lot of poking around I gave up and asked on #debian on freenode.net for suggestions. Someone asked if I had enabled the Composite extension. I hadn't of course, since I don't think it offers me anything useful, and because I didn't want to slow my system down, but it sounded like a fit for my problem. I poked around in the X server log file and found no mention of it. But then I found a X config file item online which explicitly disbles Composite, and added this to /etc/X/xorg.conf, and all my performance came back. top, dtrace, and all the kernel kwakkery you can name would not have found this problem. Log file analysis would not have found this problem, because it was not reported! A careful reexamination of configuration changes would not have found this problem because absolutely no configuration changes were made in the transition from XFree to XOrg, and because Debian offers no downgrade path for comparative analysis of the different X servers. I never switched the feature on, it was just silently enabled "for" me without any notification. However, looking at the problem, noting what was wrong, and researching it in the right ways did fix it.

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