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RPi watchdog

mcb1

I came across this very useful blog about setting the watchdog.

http://rpihouse.wordpress.com/2012/12/06/watching-the-dog/

 

It also includes information about triggering it if the load is too high.

 

cheers

Mark

Parents

  • Selsinork offered some very useful insight into the effectiveness of this approach.

    read here

     

    I'd advise a little bit of caution on relying on the load average feature of the watchdog prog.

     

    The load average is an imprecise measurement and deliberately so.  It also may not really be measuring what you'd expect.  It's an average of the number of processes either running or waiting for IO to complete. This means that you can have a high load average when you have lots of processes waiting on a slow storage device, while at the same time having a CPU utilisation that's very low and have little or no impact on system performance (assuming that slow storage device isn't your root filesystem).

     

    There's an obvious link to the Pi here, the SDcard is a slow storage device.

     

    Leaving that aside for a minute, the problem I saw with raspistill doing nothing appeared to be a problem on the GPU, or in the communication between raspistill and the GPU. It left both load average and cpu utilisation down at around zero, so the watchdog would never trigger.

     

    Watchdog timers are useful to some degree, and in some situations, but not all.

     

    With that in mind I won't be using this method in my project.

     

    Thanks

    Mark

Reply

  • Selsinork offered some very useful insight into the effectiveness of this approach.

    read here

     

    I'd advise a little bit of caution on relying on the load average feature of the watchdog prog.

     

    The load average is an imprecise measurement and deliberately so.  It also may not really be measuring what you'd expect.  It's an average of the number of processes either running or waiting for IO to complete. This means that you can have a high load average when you have lots of processes waiting on a slow storage device, while at the same time having a CPU utilisation that's very low and have little or no impact on system performance (assuming that slow storage device isn't your root filesystem).

     

    There's an obvious link to the Pi here, the SDcard is a slow storage device.

     

    Leaving that aside for a minute, the problem I saw with raspistill doing nothing appeared to be a problem on the GPU, or in the communication between raspistill and the GPU. It left both load average and cpu utilisation down at around zero, so the watchdog would never trigger.

     

    Watchdog timers are useful to some degree, and in some situations, but not all.

     

    With that in mind I won't be using this method in my project.

     

    Thanks

    Mark

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