poor fdc(4) performance

[Pyun YongHyeon]

Hi,

I encountered a P3 SMP system that shows poor fdc(4) performance.
But when I use larger block size, say 36b, it seems it works
as expected.

#dd if=boot.flp of=/dev/fd0
2880+0 records in
2880+0 records out
1474560 bytes transferred in 607.483808 secs (2427 bytes/sec)

#dd if=boot.flp of=/dev/fd0 bs=36b
80+0 records in
80+0 records out
1474560 bytes transferred in 48.482513 secs (30414 bytes/sec)

On other P4 machine I got:
#dd if=boot.flp of=/dev/fd0
2880+0 records in
2880+0 records out
1474560 bytes transferred in 51.007538 secs (28909 bytes/sec)

#dd if=boot.flp of=/dev/fd0 bs=36b
80+0 records in
80+0 records out
1474560 bytes transferred in 47.972662 secs (30738 bytes/sec)

This type of poor dd performance is the same symptom I'd like to
solve on sparc64. On ebus based Ultrasparcs it shows almost
the same phenomenon. Since I can't see any DMA or retry errors on
fdc I have no idea what caused this. In addition, it works well on
sbus based ultrasparcs which don't support DMA.
Any ideas?
-- 
Regards,
Pyun YongHyeon