[Scottish] cdrdao and CPU Usage

[Paul Millar]

On Sun, 20 Jul 2003, Phil Deane wrote:
> when I write at 16x I seem to be using 75% of my processor (an AMD XP 2000+)
> which is about that the same amount as I used when I had a p3 800. Is it 
> because I am not using buffers?

For a general "why is my computer being slow", you can't beat a good 
vmstat (I generally go for "vmstat 2", ignoring the first line).  In this 
case, the last three columns are the most relevant. They show the 
percentage of time spent in user-land, kernel-land and "idle".

If that 75% is spent in kernel, then its having difficulty reading and/or 
writing data.  Are the drives really ATAPI ones, masquerading as SCSI?  
That might be the cause of the problem.  Another possibility is somehow 
DMA for the SCSI (or IDE) channel hasn't been enabled.  Have you checked 
dmesg for things not being configured correctly?  

If instead, 75% is spent in user-land, top will show you which application
it is (but you can guess which one ;).  If this is the case, you've found
some limitation with cdrdao.  Unless there's some "don't use lots of CPU"
option, you're stuck.

I doubt any lack of buffers would be causing the problem.  Buffers only 
help if you read the same area multiple times, which I'm guessing you're 
not doing.

HTH

Paul.

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Particle Physics (Theory & Experimental) Groups                Dr Paul Millar 
Department of Physics and Astronomy                     paulm@astro.gla.ac.uk
University of Glasgow                                 paulm@physics.gla.ac.uk
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