reduce interrupt rate for CD/DVD drive(r)

Peter Jeremy peterjeremy at
Mon Aug 28 09:56:28 UTC 2006

On Sun, 2006-Aug-27 16:37:29 -0700, Jin Guojun [VFFS] wrote:
>I have difficulty to get CD/DVD write speed above 1.6MB/s  (10x for CD, 
>or 1.1x for DVD).
>The problem seems to be the interrupt rate is high (70-80% of CPU) for 
>CD/DVD drive(r).

Your drive is probably in PIO4 mode (due to there being bugs in the
UDMA implementation on many drives).  Check hw.ata.atapi_dma and
"atacontrol mode acd0".  You may find you can change to WDMA2 mode
which will significantly reduce the interrupt and CPU load.  You will
need to do some experimenting with your drives to see what works for

Peter Jeremy
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