High Interrupt rate since r279961 on STABLE/10 branch

[Yanhui Shen]

Hi,

I noticed the interrupt rate of my FreeBSD system is very high (~35%) after
upgrade from r279138 to r284205.

To find out which revision cause this problem,
I used a  binary search manner and compiled the kernel 11 times.
Finally I located to r279961, the interruption rate is abnormal since this
revision.

Do you have any idea about this issue?

( I'm temporarily using r279958 kernel with r284205 base system, everything
is fine.)

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Device: ThinkPad R400 (Product ID: 278225C)
CPU: Intel Core 2 Duo processor T6570 (2.1 GHz)
GPU: Intel Integrated Graphics 4500MHD

Output of "vmstat -i" with r284205 kernel (abnormal):
interrupt                    total              rate
irq1: atkbd0              1607             1
irq9: acpi0                 131958         104
irq12: psm0               4281            3
irq16: uhci3               239899376  189643
irq20: hpet0 uhci0     1426118      1127
irq21: uhci1               40315          31
irq23: ehci0               33                0
irq256: vgapci0          6059           4
irq257: em0               49220         38
irq258: hdac0            62                0
irq260: ahci0:ch0       17217          13
irq261: ahci0:ch1       23               0
Total                          241576269  190969

Output of "vmstat -i" with r279958 kernel (normal):
interrupt                          total       rate
irq1: atkbd0                       48155          3
irq9: acpi0                      1581468        105
irq12: psm0                       209484         13
irq19: ehci1                       48099          3
irq20: hpet0 uhci0              17385585       1156
irq21: uhci1                      680884         45
irq23: ehci0                          31          0
irq256: vgapci0                  2611430        173
irq257: em0                      1342009         89
irq258: hdac0                     602220         40
irq260: ahci0:ch0                 236313         15
irq261: ahci0:ch1                     27          0
Total                           24745705       1646

The revision:
https://svnweb.freebsd.org/base?view=revision&revision=279961

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Best regards,
Yanhui Shen