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DMA, kernel 2.6.6 and CD/DVD

Is there a known problem with DMA for CD and DVD drives with the 2.6.6

On my G3 iBook (600MHz) I am getting very high CPU usage with copying
from a DVD or CD, "cp /dev/hdb /dev/null" results in 100% CPU usage with
about 80% being "iowait". hdparm indicates that DMA is enabled. I also
get very low throughput rates (hdparm -t) especially for writable media
where they are 5-600 kB/sec.

ephiny:~# hdparm -i /dev/hdb


 Model=SONY CD-RW CRX800E, FwRev=1.3g, SerialNo=
 Config={ Fixed Removeable DTR<=5Mbs DTR>10Mbs nonMagnetic }
 RawCHS=0/0/0, TrkSize=0, SectSize=0, ECCbytes=0
 BuffType=unknown, BuffSize=0kB, MaxMultSect=0
 (maybe): CurCHS=0/0/0, CurSects=0, LBA=yes, LBAsects=0
 IORDY=on/off, tPIO={min:180,w/IORDY:120}, tDMA={min:120,rec:120}
 PIO modes:  pio0 pio1 pio2 pio3 pio4
 DMA modes:  mdma0 mdma1 *mdma2

 * signifies the current active mode

While copying from DVD a typical summary line from top is:
top - 10:03:27 up 34 min,  1 user,  load average: 0.29, 0.18, 0.19
Tasks:  87 total,   1 running,  86 sleeping,   0 stopped,   0 zombie
Cpu(s): 15.5% us,  6.9% sy,  0.0% ni,  0.0% id, 75.7% wa,  2.0% hi, 
0.0% si
Mem:    386172k total,   272452k used,   113720k free,    41680k buffers
Swap:   515564k total,        4k used,   515560k free,   129496k cached

The kernel is the current debian 2.6.6-powerpc package.

Any suggestions?

| James Tappin           | School of Physics & Astronomy |  O__    |
| sjt@star.sr.bham.ac.uk | University of Birmingham      | --  \/` |
| Ph: 0121-414-6462. Fax: 0121-414-3722                  |         |

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