Qustions about CPU usage of "dd" process

[Shane Huang]

Greetings:

This is Shane, I'm sorry to disturb you guys.

I have some questions which are about CPU usage percentage of "dd"
process.
I'm appreciated if you can give me some help or suggestion.

When we do some test on our motherboards, we find that in some cases,
the CPU usage percentage of "dd" is a little high when we dump data
from SATA ODD DVD disc to SATA HDD:
# dd if=/dev/cdwriter of=/root/temp.iso

The CPU percentage of "dd" process sometimes is 30% to 50%,
which is higher than we expect (<= 20%), and there is no other big
program running at the same time.
If the disc in SATA ODD is CD-R instead of DVD-R, the percentage is
much smaller(<=20).

So my questions are:
(1) Is there an official normal range(or criteria) to the "dd" CPU
percentage?
(2) Can we say that it's abnormal if it is higher than 30% or even 50%?
(3) And what kinds of factors lead to the high CPU percentage of "dd"
and
how to decrease it?


BTW, my HW/SW Env:
AMD SB700 + RS690
SAMSUNG SATA ODD
Seagate SATA HDD
RedHat RHEL5/RHEL4.6 and openSUSE10.3 Linux


Thanks
Best Regards
Shane