poor 164SX IDE drive performance, dma enabled

["Gregory P. Smith" <greg@electricrain.com>]

I have a 164SX (533mhz 21164PC, the tiny cache "celeron" of 21164s...)
and have been using it with uw-scsi drives for the past three years.
The scsi drives perform great (10mbyte/sec).

I recently added a modern 60gb IDE disk.  The drive does work in this
machine but it maxes out at 3mbytes/sec, pegging the CPU in the process.
I am currently running a 2.4.20-pre9 kernel.  The ide drivers were
compiled as modules and I do have DMA and 32-bit I/O enabled using hdparm:

/dev/hdc:
 multcount    = 16 (on)
 I/O support  =  1 (32-bit)
 unmaskirq    =  0 (off)
 using_dma    =  1 (on)

Does the 164SX motherboard chipset not actually do DMA or is the source of
my speed problem elsewhere (limitation of the 164sx & 21164pc perhaps)?
If the motherboard chipset doesn't cut it, has anyone had better
performance with a PCI card?

TIA,
-g