Is it normal for dd to take 20-25% cpu time (as reported by top)?  Preclear is in first phase - pre-read @ 145-160MB/s according to the active script.  Pre-clearing one 1T sata drive.

 

Update:  on step 2 of 10 (writing zeroes), dd is at 38.7% cpu, idle is 9.3% with 48% wait, and CPU is at 800MHz. Sysload is 2.43, 2.47, 2.54.  I have another post about the CPU being at 800 and bouncing up to 2700 (full speed), but even when loaded it stays for the most part at 800.

 

5.0-rc8a

Asus M5A78L-MLX Plus, 8GB, Sempron 140

 

Sounds ok to me.

 

Remember, if it was a perfect CPU only process (calculating the first million digits of PI for example  ), and there were no other processes competing for time, then it would get 100% of the CPU and never relinquish it unless another process needed some CPU time as well.  Since the preclear process seems to be waiting on the disk 48% of the time, and therefore not using CPU, the 38% sounds about right.  When reading from the disk using "dd" it is simultaneously writing to /dev/null, and it is doing it as fast as your CPU allows.

 

Linux will apportion the CPU to those processes waiting to use it and are in a "ready to run" status.  A process that is waiting on a resource (like waiting on disk I/O) does not use CPU.  You can think of it as "sleeping" until the resource becomes available.    Your server was probably idle otherwise, with just a little bit of CPU and I/O used by the "top" command itself.

 

Joe L.