Experimental Physics and
Industrial Control System

Marty Kraimer <[email protected]> · Fri, 27 Apr 2001 08:44:10 -0500

I have had some private message with Andy about this problem. We are making
changes to devVXStats to fix the problem. As soon as we have done some more
testing I will make the new code available. Andy also reports that the new
algorithm for computing cpu usage is more stable.

The crash did not happen on 68xxx processors because floating point exceptions
were not trapped. On the powerPC they are trapped.

Marty Kraimer

Andy Foster wrote:
> 
> 
> 
>   --------------------------------------------------------------------------------
> Dear All,
> 
> Has anyone experienced a task crash caused by the "devVXStats" support
> in 3.13.4?
> 
> I have just added the database records for this. I'm running on
> an MVME2700 PPC. The system is apparently about 7% loaded according
> to the report from the device support. I'm sampling the CPU load every
> 5 seconds, although I have varied this with the same outcome.
> 
> I traced the crash to line 373 of "devVXStats.c" (in the function "getCpu"):
> 
> temp = 100.0 * temp/ticksNow;
> 
> It appears to be possible for "ticksNow" to be 0 at this point.
> 
> I added a conditional check on "pcpuUsage->ticksNow" so that the code
> only gets executed if this value is non-zero (adding a printf statement so
> that I could see how many crashes I would have had):
> 
> static double getCpu()
> {
>     if((pcpuUsage->didNotComplete && pcpuUsage->nBurnNow==0) || !pcpuUsage->ticksNow) {
>         if( !pcpuUsage->ticksNow )
>           printf("This would have been a crash\n");
>         pcpuUsage->usage = 0.0;
>     } else {
>         double temp;
>         double ticksNow,nBurnNow;
> 
>         ticksNow = (double)pcpuUsage->ticksNow;
>         nBurnNow = (double)pcpuUsage->nBurnNow;
>         ticksNow *= (double)pcpuUsage->nBurnNoContention/nBurnNow;
>         temp = ticksNow - (double)pcpuUsage->ticksNoContention;
>         temp = 100.0 * temp/ticksNow;
>         if(temp<0.0 || temp>100.0) temp=0.0;/*take care of tick overflow*/
>         pcpuUsage->usage = temp;
>     }
>     pcpuUsage->didNotComplete = TRUE;
>     semGive(pcpuUsage->startSem);
>     return(pcpuUsage->usage);
> }
> 
> I saw the statement about 4 times in 1 hour on the console.
> I'm not sure why "pcpuUsage->ticksNow" is zero, but I think it might be
> worth adding in the check just to be defensive.
> 
> Cheers,
> 
> Andy
> 
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System