hdparm shows poor performance on cached reads for PATA drive

[Konstantin Svist]

Answering my own question

After some more digging: apparently the resource hog was wdaemon (daemon 
that emulates a drawing tablet so that it can be hotplugged into X).
This was a surprise since my new laptop also has the same one installed 
- and doesn't exhibit the slowdown.
I've emailed the maintainer and asked him to check out the problem.

Another service that affected the speed was cpuspeed - but that's only 
when "performance" was not selected as the current profile.