CD and 2.6 - more data fewer answers

[Bill Davidsen <davidsen@tmr.com>]

I have a 2.6.7-rc1-mm1 test system with both IDE CD and USB CD-R. Both 
work fine as I normally use them, the CD-R is my primary backup device.

With all the discussion of DMA or not DMA, I decided to try some 
reads... I tried readcd using /dev/hdc and the user was 60%, sys 40%, no 
idle. Using ATAPI:0,0,0 I saw user 60%, sys 2% idle 38%. Then using the 
USB device I saw user 4%, sys 9%, idle 12%, wio 75%. The USB is much 
faster, so this looked right, and it appeared that on data reads DMA was 
being used. I have no idea where all the user CPU was going.

Then I turned on -c2scan to read 2352 byte sectors without the final 
error correct. With /dev/hdc I saw use 42%, sys 68%. Using ATAPI:0,0,0 I 
saw user 47%, sys 53%. And using the USB device the c2scan ended without 
reading any data.

The difference between /dev/hdc and ATAPI:0,0,0 is small, although 
consistent. The access by SCSI number failed with the USB drive, and 
/dev/scd0 resulted in "readcd: Invalid argument. Cannot get SCSI I/O 
buffer" when tried (yes, as root as well).

I make no claim that this sheds light on the question, just a sprinkle 
of data to provide flavor. I'll bring in an audio CD tomorrow and see 
what trying to rip that does, unless someone beats me to it.

-- 
    -bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
  last possible moment - but no longer"  -me