ciss(4): speed degradation for Compaq Smart Array

We have several Proliants DL380 with integrated Smart Array 5i controller,
with installed FreeBSD OS versions 4.11-stable, 5.4-pre and 6.0-current.
All systems have disks configured as RAID5.

I've noticed there is drastic difference in speed for the systems.
While I have linear transfer 45-50 Mb/s (write) and 100 Mb/s (read)
for FreeBSD 4.11, there is near two times degradation in speed
with 5.4 and 6.0.

-- 8< ------------------------------------------------------------------

FreeBSD 4.11:
ciss.c,v 1.2.2.21 2005/01/21

# dd if=/dev/zero of=/var/tmp/4G bs=1024 count=$[4*1024*1024]

4294967296 bytes transferred in 107.075789 secs (40111470 bytes/sec)

# dd if=/var/tmp/4G of=/dev/zero

4294967296 bytes transferred in 42.394322 secs (101309966 bytes/sec)


FreeBSD 5.4-pre:
ciss.c,v 1.56.2.1 2005/01/20

# dd if=/dev/zero of=/var/tmp/4G bs=1024 count=$[4*1024*1024]

4294967296 bytes transferred in 163.088095 secs (26335259 bytes/sec)

# dd if=/var/tmp/4G of=/dev/zero

4294967296 bytes transferred in 79.773797 secs (53839324 bytes/sec)


FreeBSD 6.0:
ciss.c,v 1.60 2005/03/29

# dd if=/dev/zero of=/var/tmp/4G bs=1024 count=$[4*1024*1024]

4294967296 bytes transferred in 224.804547 secs (19105340 bytes/sec)

# dd if=/var/tmp/4G of=/dev/zero

4294967296 bytes transferred in 94.839699 secs (45286598 bytes/sec)

-- 8< ------------------------------------------------------------------

These are simple tests taken on running systems (tests in single user
mode are slightly different but of the same order)

It seems, there is sensible speed penalty with driver version growing.

Andrey