i386/61646: Strange irq20 weirdness causing system load

[Yevgeniy Aleynikov]

>Number:         61646
>Category:       i386
>Synopsis:       Strange irq20 weirdness causing system load
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    freebsd-i386
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Tue Jan 20 12:20:14 PST 2004
>Closed-Date:
>Last-Modified:
>Originator:     Yevgeniy Aleynikov
>Release:        5.2-RELEASE made with make world from CVS
>Organization:
none
>Environment:
FreeBSD gate.home 5.2-RELEASE FreeBSD 5.2-RELEASE #1: Sat Jan 17 00:25:19 PST 2004     eugene at gate.home:/.1/obj/.1/src/sys/gate2  i386

>Description:
After upgrade from 5.1 to 5.2 my system became very slow, spending alot of time for IRQ20 interrupts (which is probably routed to timer interrupt).
Here's top output in idle system state:
last pid: 17584;  load averages:  0.26,  0.28,  0.30    up 2+20:11:35  12:06:17
65 processes:  1 running, 64 sleeping
CPU states:  0.2% user,  0.0% nice,  0.8% system, 46.7% interrupt, 52.3% idle
Mem: 63M Active, 306M Inact, 80M Wired, 24M Cache, 60M Buf, 22M Free
Swap: 512M Total, 80K Used, 512M Free

  PID USERNAME PRI NICE   SIZE    RES STATE  C   TIME   WCPU    CPU COMMAND
17584 xxxxxx   -52    0  2288K  1400K CPU0   0   0:00  1.54%  0.15% top


Here's systat output:

                    /0   /1   /2   /3   /4   /5   /6   /7   /8   /9   /10
     Load Average   ||

                    /0   /10  /20  /30  /40  /50  /60  /70  /80  /90  /100
root     irq20: acp XXXXXXXXXXXXXXXXXX
root     idle: cpu0 XXXXXXXXXXX
root     idle: cpu1 XXXXXXXXXX
             <idle> XXXXXXXXXX


> vmstat -i
interrupt                          total       rate
irq4: sio0                           115          0
irq5: sbc0                         10479          0
irq6: fdc0                             5          0
irq8: rtc                       31431572        128
irq14: ata0                       299080          1
irq16: sis0                      2856265         11
irq17: ed0                       2726682         11
irq18: ahc0                          270          0
irq19: uhci0                           2          0
irq20: acpi0                  2548283659      10377
irq0: clk                       24555474         99
Total                         2610163603      10629


Here's lines from dmesg.boot:

ACPI APIC Table: <ASUS   P2B-D   >
FreeBSD/SMP: Multiprocessor System Detected: 2 CPUs
 cpu0 (BSP): APIC ID:  1
 cpu1 (AP): APIC ID:  0
ioapic0 <Version 1.1> irqs 0-23 on motherboard
Pentium Pro MTRR support enabled
npx0: [FAST]
npx0: <math processor> on motherboard
npx0: INT 16 interface
acpi0: <ASUS   P2B-D   > on motherboard
acpi0: Overriding SCI Interrupt from IRQ 9 to IRQ 20

Let me know if you need more info.
>How-To-Repeat:
Boot system, watch system (interrupts) load.
>Fix:
None
>Release-Note:
>Audit-Trail:
>Unformatted: