I just took ran iostat before and after a cold KDE startup, on my Dell Precision 390 (Core 2 Duo, 4 GB RAM, 750 GB SATA hard disk).

The output indicated (I think?) that about 197120 blocks, or 770 MB, were read during KDE start. I think this is probably accurate, since there's not going to be any thrashing with 4 GB of RAM.

Anyway, 770 MB is not a lot for this monster desktop, but for my netbook it's huge. So I'm wondering how much of this stuff getting read is actually necessary, and how much is related to functionality I don't need. It seems to me that, on laptops with relatively slow HDDs, I could make KDE more usable by turning off the most I/O intensive parts of it.

So... What parts of KDE (that can actually be disabled) are likely to be the biggest source of read operations?

First parts to look at would be Akonadi and Nepomuk, if they are installed - as they both invoke database servers (MySQL and Virtuoso respectively) which will be disk intensive.

Thanks. In this case Nepomuk was already turned off entirely. Akonadi was running, but didn't seem to be eating much in the way of resources.

Anyway I've managed to get some improvement in KDE 4 performance...
- The biggest impact was from running 'e2fsck -D' on my partitions. Sounds simple, but it reduced total boot time by about 10 seconds on my netbook.
- Using writeback rather than ordered journaling mode with ext4 seems to do something as well, but certainly not to the same extent.

KDE definitely seems to perform better overall after a directory optimization, which makes me wonder if it's doing something with lots of nested directories, or enumerating lots of files somewhere. Maybe that would account for some of the reads? Don't know, I'm not a filesystem expert.

I bet you'd like http://e4rat.sourceforge.net/

The file/folder structure under /usr may definitely qualify as having many directories, and while KDE will not scan all of them, it may indeed scan many of them.