kern/46099: Disk I/O slowness on Dell R310 + SAS6/iR

[pettai%nordu.net@localhost]

>Number:         46099
>Category:       kern
>Synopsis:       Disk I/O slowness on Dell R310 + SAS6/iR
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat Feb 25 23:50:00 +0000 2012
>Originator:     Fredrik Pettai
>Release:        NetBSD 6.0_BETA i386
>Organization:
NORDUnet
>Environment:
NetBSD authn1.nordu.net 6.0_BETA NetBSD 6.0_BETA (GENERIC) i386
>Description:
Disk access on my new R310 with PERC 6/i is slowish. 

During the boot, this appears:
...
mpt has not been converted to device_t
mpt0 at pci1 dev 0 function 0: vendor 0x1000 product 0x0058 (rev. 0x08)
mpt0: interrupting at ioapic0 pin 16
mpt0: Phy 0: Link Rate 3.0 Gbps
mpt0: Phy 1: Link Rate 3.0 Gbps
mpt0: Unknown async event: 0xb
scsibus0 at mpt0: 112 targets, 8 luns per target
...
sd0 at scsibus0 target 0 lun 0: <Dell, VIRTUAL DISK, 1028> disk fixed
sd0: 931 GB, 953344 cyl, 16 head, 128 sec, 512 bytes/sect x 1952448512 sectors
sd0: async, 8-bit transfers, tagged queueing
probe(mpt0:0:8:0): generic HBA error

Also see
http://mail-index.netbsd.org/netbsd-users/2011/06/21/msg008461.html
>How-To-Repeat:
Just install/run NetBSD on a Dell (R310) with a SAS 6/iR controller.

Also see
http://mail-index.netbsd.org/netbsd-users/2011/06/21/msg008461.html
>Fix: