high interrupts load xhci

Hello.
I have a very high interrupts load on my FreeBSD machine. It happens when I plug any USB device (like a keyboard), and the load is still high after disconnecting the device. It becomes normal after reboot.
My system based on ASUS P8Z68-V Pro/Gen3 motherboard.
MYKERNEL is the GENERIC kernel with ipfw support.

Sorry for bad English.
Some debug information below:

# uname -a
FreeBSD servergate 9.0-RELEASE FreeBSD 9.0-RELEASE #0: Wed Mar 28 15:00:36 MSK 2012 root_at_servergate:/usr/src/sys/amd64/compile/MYKERNEL amd64

# vmstat -i
interrupt                          total       rate
irq16: xhci1                 12027577930      19620
irq23: ehci0 ehci1               1853306          3
cpu0:timer                     628564836       1025
irq256: em0:rx 0                56064005         91
irq257: em0:tx 0                43550786         71
irq258: em0:link                       2          0
irq262: em2:rx 0               553904449        903
irq263: em2:tx 0               512166987        835
irq264: em2:link                       1          0
irq265: em3:rx 0               308737867        503
irq266: em3:tx 0               607085499        990
irq268: ahci0                    5885008          9
cpu1:timer                     130146122        212
cpu3:timer                     103306335        168
cpu2:timer                      60072912         97
Total                        15038916045      24533


# sysctl hw.usb.xhci.debug=16 ; sleep 1; sysctl hw.usb.xhci.debug=0

/var/log/messages

Oct  1 12:46:28 servergate kernel: xhci_interrupt: real interrupt (sts=0x00000000, iman=0x00000002)

Oct  1 12:46:29 servergate last message repeated 4239 times


# sysctl hw.usb.xhci.debug=16 ; sleep 2 ; sysctl hw.usb.xhci.debug=0
/var/log/messages
Oct  1 12:47:42 servergate last message repeated 8490 times

# systat -vmstat
    1 users    Load  0.63  0.55  0.55                  Oct  1 13:41

Mem:KB    REAL            VIRTUAL                       VN PAGER   SWAP PAGER
        Tot   Share      Tot    Share    Free           in   out     in   out
Act 1485876  159184  5740552   176552 2857720  count
All 1585844  165036 1079661k   210368          pages
Proc:                                                            Interrupts
  r   p   d   s   w   Csw  Trp  Sys  Int  Sof  Flt        cow    175k total
            140      353k   41  938 172k 1044    3      2 zfod   165k xhci1 16
                                                          ozfod     3 ehci0 ehci
0.1%Sys  17.0%Intr  0.0%User  0.0%Nice 82.9%Idle        %ozfod  1127 cpu0:timer
|    |    |    |    |    |    |    |    |    |    |       daefr   809 em0:rx 0
+++++++++                                                 prcfr   473 em0:tx 0
                                        41 dtbuf        2 totfr       em0:link
Namei     Name-cache   Dir-cache    204931 desvn          react  1496 em2:rx 0
   Calls    hits   %    hits   %    172501 numvn          pdwak  1537 em2:tx 0
     391     385  98                 49267 frevn          pdpgs       em2:link
                                                          intrn  1339 em3:rx 0
Disks  ada0  ada1 pass0 pass1                      875960 wire   2201 em3:tx 0
KB/t  30.73 30.73  0.00  0.00                     1122584 act       9 ahci0 268
tps       4     4     0     0                     3145672 inact   962 cpu1:timer
MB/s   0.13  0.13  0.00  0.00                         276 cache   254 cpu3:timer
%busy     0     0     0     0                     2857444 free    105 cpu2:timer
                                                   837152 buf

# pciconf -lv
hostb0_at_pci0:0:0:0: class=0x060000 card=0x844d1043 chip=0x01008086 rev=0x09 hdr=0x00
vendor = 'Intel Corporation'
device = '2nd Generation Core Processor Family DRAM Controller'
class = bridge
subclass = HOST-PCI
- - - - -
xhci0_at_pci0:4:0:0: class=0x0c0330 card=0x84881043 chip=0x10421b21 rev=0x00 hdr=0x00
vendor = 'ASMedia Technology Inc.'
device = 'ASM1042 SuperSpeed USB Host Controller'
class = serial bus
subclass = USB
- - - - -
xhci1_at_pci0:7:0:0: class=0x0c0330 card=0x84881043 chip=0x10421b21 rev=0x00 hdr=0x00
vendor = 'ASMedia Technology Inc.'
device = 'ASM1042 SuperSpeed USB Host Controller'
class = serial bus
subclass = USB