Re: NMI watchdog not ticking at the right intervals

[Corey Minyard <minyard@acm.org>]

Mikael Pettersson wrote:

>On Fri, 25 Oct 2002 09:09:10 -0500, Corey Minyard wrote:
>  
>
>>As I have been working on my NMI patch, I have noticed that the NMI 
>>watchdog does not seem to be ticking correctly.  I've tried 2.4 and 2.5 
>>kernels, and I get the same results.  From my reading of the code, it 
>>should tick once a second.  However, I have had the time between ticks 
>>vary from around 33 to over 100 seconds.  Tbe time between ticks is 
>>different on every boot, but is consistent once booted.  Is there some 
>>divider register that's not getting initialized?
>>
>>Here's my cpuinfo:
>>
>>processor    : 0
>>cpu_package    : 0
>>vendor_id    : GenuineIntel
>>cpu family    : 6
>>model        : 11
>>model name    : Intel(R) Pentium(R) III Mobile CPU      1066MHz
>>    
>>
>
>(Me thinks "speedstep?")
>
>Do you boot with nmi_watchdog=1 or 2?
>
It's set to 2 (local APIC).  Actually, when I set it to 1 (in 2.5) the 
code overrides it and sets it to 2.  But 2 is what it is running with now.

>The perfctr + local-APIC driven NMI watchdog is dependent
>on the CPU's clock frequency. If this changes, the NMI rate
>will change accordingly.
>
>The NMI rate may also be affected by APM/ACPI and how often
>the kernel executes HLT.
>
This board is not doing speed stepping.  It's running derated for 
reliability.

But that makes me think of something...

If I put a program into an infinite loop, then it will step every second 
like it is supposed to.  That makes sense now.

Thanks,

-Corey