[Voyage-linux] Bug reports

[Punky Tse]

Hi all,

Back to this issue again.  Very strange findings.

I notices that when I use 3.2.x kernel with "console=ttyS0,38400n8", I 
can see the idle counter is not moving in 100 ticks so "vmstat 1" would 
yield floating point exception.  If I remove "console=..." parameter, it 
moves at 100 ticks.

Further compare the dmesg of the two boots, I see the problem is lies on 
clocksource setting to pit.  With "console=ttyS0,38400n8", clocksource 
is adjusted to pit.  If without, clocksource is set to tsc.

So now, with "console=ttyS0,38400n8", I manually set clocksource=tsc, 
idle counter now moves at 100 ticks, and vmstat 1 runs normally.

     echo "tsc" > 
/sys/devices/system/clocksource/clocksource0/current_clocks

Strange?   The next question is, why console=... parameter affects 
clocksource selection?

Regards,
Punky

On 3/13/2012 2:29 PM, Kim-man 'Punky' TSE wrote:
> Hi Stanislav,
>
> Regarding to the 1st problem: "Floating point exception" in "vmstat 1" 
> when idle.  I am able to reproduce it yesterday.
>
> But after I reboot with different kernels back and forth, today this 
> problem disappears automagically!  I have debugged a bit and can share 
> the finding
>
> It seems that on ALIX with 3.2 kernel, the idle counter in /proc/stat 
> (the 4th number) is not moving at 100 ticks when idle.  I once saw the 
> idle counter stay as the same number when it is idle.  If the idle 
> counter does not change over an interval, vmstat would use 0 for a 
> divisor.  So the floating point exception is actually division-by-zero 
> error.
>
> The below output shows the correct behaviour
>
> while [ 1 ] ; do cat /proc/stat |grep "cpu  " ; sleep 1 ; done
> cpu  1031 0 1916 1115462 258 13 73 0 0 0
> cpu  1032 0 1917 1115560 258 13 73 0 0 0
> cpu  1032 0 1919 1115658 258 13 73 0 0 0
> cpu  1033 0 1920 1115756 258 13 73 0 0 0
>
> Next, I will do a hard reset on ALIX board to see if I can repeat the 
> problem.
>
>
> On 3/5/2012 10:13 PM, Stanislav Sinyagin wrote:
>> hi,
>>
>> is there a plan to use a bug tracking software, like Bugzilla or 
>> JIRA? I've got a couple of bugs to report:
>>
>> 1. With voyage-current, as of about a week ago, "vmstat 1" was 
>> crashing when the host was idle (ALIX board).
>>
>


-- 

Regards,
Kim-man "Punky" Tse

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