[parisc-linux] C3000 and IDE DMA support

[M. Grabert]

On Wed, 27 Aug 2003, Grant Grundler wrote:

> On Wed, Aug 27, 2003 at 11:22:54PM +0100, Alan Cox wrote:
> > Nod.. I'm trying to fathom the 3Mbyte/second behaviour while hdparm
> > claims DMA is on
>
> I thought each PIO READ costs something like 400 or 500 cycles on c3k
> (400Mhz CPU).  400/3 == 133 cycles/byte.
>
> Either doing very slow DMA or 32-bit (4*133 == 532) reads.
> Then it would make sense.

beast:/home/xam# hdparm -c /dev/hda

/dev/hda:
 IO_support   =  1 (32-bit)


Well, I set it to 32bit I/O, more specifically I also tried
c=0 (16bit, default), c=3 (32-bit with sync). Everytime the same:


beast:/home/xam# hdparm -Tt /dev/hda

/dev/hda:
 Timing buffer-cache reads:   128 MB in  1.80 seconds = 71.11 MB/sec
 Timing buffered disk reads:  64 MB in 20.48 seconds =  3.12 MB/sec


However switching of DMA (as I told in my previous post, 'hdparm -d 0')
will cause a kernel crash (+ dump).

I haven't tried to compile & test a kernel without DMA support (or NS87415
support)


greetings, Max