[ltp] CPU running – but why?…

[Arno Trautmann]

Hi,

some times now it happened that my CPUs were running nearly 50% in C0,
the rest in C3 – but no prgramm was active, and there was absolutely no
reason for high CPU activity. The CPUs heated up over 70°C (I didn’t 
wait to see how high it would get, but shut down the system then), while 
they normally are at 40–50°C. Also, sometimes when this happens, the
frequency is at 1200MHz instead of the expected 800MHz.

I’m running Arch Linux on a X61s, using speedstep; normally, the CPUs
are in C3 for about 95%, 800MHz:
---
Cn                Avg residency       P-states (frequencies)
C0 (cpu running)        ( 4.8%)         1.61 Ghz     0.0%
C1                0.0ms ( 0.0%)         1.60 Ghz     0.0%
C2                0.0ms ( 0.0%)         1200 Mhz     0.0%
C3                3.9ms (95.2%)          800 Mhz   100.0%
---
When it is heating up, powertop gives me something like:
---
Cn                Avg residency       P-states (frequencies)
C0 (cpu running)        (42.1%)         1.61 Ghz     0.0%
C1                0.0ms ( 0.0%)         1.60 Ghz     1.4%
C2                0.0ms ( 8.3%)         1200 Mhz     0.0%
C3                0.0ms (49.6%)          800 Mhz    98.6%


Wakeups-from-idle per second : 16359.3  interval: 5.0s
no ACPI power usage estimate available

Top causes for wakeups:
   35.8% ( 87.8)      <kernel IPI> : Rescheduling interrupts
   26.2% ( 64.2)       firefox-bin : schedule_timeout (process_timeout)
   19.2% ( 47.0)       <interrupt> : HDA Intel, ohci1394
    7.4% ( 18.2)       <interrupt> : extra timer interrupt
    7.3% ( 18.0)       <interrupt> : acpi
---
and the output of top:
---
top - 21:06:04 up  1:18,  1 user,  load average: 0.40, 0.27, 0.21
Tasks:  86 total,   2 running,  84 sleeping,   0 stopped,   0 zombie
Cpu(s):  6.0%us,  0.6%sy,  0.0%ni, 93.4%id,  0.0%wa,  0.0%hi,  0.0%si,
0.0%st
Mem:   1009680k total,   558744k used,   450936k free,    27964k buffers
Swap:  1461872k total,        0k used,  1461872k free,   199776k cached

   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND

2840 arno      20   0  532m 152m  27m S    6 15.5  10:15.16 firefox-bin
2707 root      20   0  361m  47m 7924 S    3  4.8   2:33.98 Xorg
2796 arno      20   0 41852  10m 7416 S    0  1.1   0:01.62 xfce4-mixer
2798 arno      20   0 44388  15m 9456 R    0  1.6   0:01.29 terminal
3102 root      20   0  2132 1040  816 R    0  0.1   0:00.04 top
---
Most time everything is absolutely fine, and this behaviour is not
reproduceable. Can anyone give me a hint what could cause this? [Happens 
both when on AC and on battery]

Thanks,
Arno