5.3-RC1 poor ATA perfomance

Hi!

I have hit a very strange problem with a poor ata perfomance.

First some numbers:
=== FreeBSD 5.3-RC1
# dd if=/dev/ad0 of=/dev/null bs=1m count=512
536870912 bytes transferred in 23.891834 secs (22470896 bytes/sec)
# dd if=/dev/zero of=/dev/ad0s1 bs=1m count=512
536870912 bytes transferred in 35.413467 secs (15160078 bytes/sec)

=== Linux 2.6.8-1 (OpenBSD also gives similar numbers)
# dd if=/dev/hda of=/dev/null bs=1M count=512
536870912 bytes transferred in 22.272891 seconds (24104231 bytes/sec)
# dd if=/dev/zero of=/dev/hda1 bs=1M count=512
536870912 bytes transferred in 23.574157 seconds (22773706 bytes/sec)

As you see the writing is quite slower.

Some details on hardware:
atapci0: <Intel ICH4 UDMA100 controller> port 0x1860-0x186f,0x376,
0x170-0x177,0x3f6,0x1f0-0x1f7 at device 31.1 on pci0
ata0: channel #0 on atapci0
ad0: 38154MB <TOSHIBA MK4021GAS/GA224A> [77520/16/63] at ata0-master UDMA100

ad1 is absent.

-- 
Best regards,
  Alexander.