High CPU utilization even with DMA enabled?

[Dan Nelson]

In the last episode (May 07), Andre Guibert de Bruet said:
> Here's the output of top while moving a large file from one disk to
> another on my otherwise idle desktop machine:
> 
>   PID USERNAME    PRI NICE   SIZE    RES STATE  C   TIME   WCPU    CPU COMMAND
>    26 root        -68 -187     0K    12K WAIT   0 141:36 79.98% 79.98% irq7: dc0 ohci0

Is this line truncated?  If not, your CPU load is caused by either
your network card or your USB interface, not your file copy.

>    24 root        -64 -183     0K    12K WAIT   0   0:27  1.22%  1.22% irq15: ata1

> Now, I realize that copying a file from one disk to another requires cpu
> cycles even with DMA enabled, but is 80% of cpu usage to be expected?
> Also, wouldn't one expect process id 24 (irq15: ata1) to be using CPU
> during such transfers?

It is; I'd even call 1.22% cpu load a bit high, although I have no IDE
systems to compare it against.  All it's doing is DMA'ing data.

-- 
	Dan Nelson
	dnelson at allantgroup.com